Migrate filesystem clients to broker

[Weidong Cui (wdcui)]

This PR moves LiteBox filesystem access behind the broker-owned file service by wiring file RPCs into the guest resolver, constructing authoritative Linux and Windows broker filesystems, requiring broker connections in production shims and runners, and migrating registry, loader, mmap, and test paths to the production broker transport while preserving existing filesystem behavior.

[github-actions]

🤖 SemverChecks 🤖 ⚠️ Potential breaking API changes detected ⚠️

Click for details

--- failure enum_missing: pub enum removed or renamed ---

Description:
A publicly-visible enum cannot be imported by its prior path. A `pub use` may have been removed, or the enum itself may have been renamed or removed entirely.
        ref: https://doc.rust-lang.org/cargo/reference/semver.html#item-remove
       impl: https://github.com/obi1kenobi/cargo-semver-checks/tree/v0.50.0/src/lints/enum_missing.ron

Failed in:
  enum litebox::fs::FileType, previously in file /home/runner/work/litebox/litebox/target/semver-checks/git-ulitebox/a813a7f2b26a346df12a5496b298b75bc3edb3c9/litebox/src/fs/mod.rs:158

--- failure module_missing: pub module removed or renamed ---

Description:
A publicly-visible module cannot be imported by its prior path. A `pub use` may have been removed, or the module may have been renamed, removed, or made non-public.
        ref: https://doc.rust-lang.org/cargo/reference/semver.html#item-remove
       impl: https://github.com/obi1kenobi/cargo-semver-checks/tree/v0.50.0/src/lints/module_missing.ron

Failed in:
  mod litebox::fs::resolver, previously in file /home/runner/work/litebox/litebox/target/semver-checks/git-ulitebox/a813a7f2b26a346df12a5496b298b75bc3edb3c9/litebox/src/fs/resolver.rs:4

--- failure struct_missing: pub struct removed or renamed ---

Description:
A publicly-visible struct cannot be imported by its prior path. A `pub use` may have been removed, or the struct itself may have been renamed or removed entirely.
        ref: https://doc.rust-lang.org/cargo/reference/semver.html#item-remove
       impl: https://github.com/obi1kenobi/cargo-semver-checks/tree/v0.50.0/src/lints/struct_missing.ron

Failed in:
  struct litebox::fs::resolver::Resolver, previously in file /home/runner/work/litebox/litebox/target/semver-checks/git-ulitebox/a813a7f2b26a346df12a5496b298b75bc3edb3c9/litebox/src/fs/resolver.rs:25
  struct litebox::fs::resolver::Context, previously in file /home/runner/work/litebox/litebox/target/semver-checks/git-ulitebox/a813a7f2b26a346df12a5496b298b75bc3edb3c9/litebox/src/fs/resolver.rs:73
  struct litebox::fs::resolver::ResolvedPath, previously in file /home/runner/work/litebox/litebox/target/semver-checks/git-ulitebox/a813a7f2b26a346df12a5496b298b75bc3edb3c9/litebox/src/fs/resolver.rs:151

--- failure enum_missing: pub enum removed or renamed ---

Description:
A publicly-visible enum cannot be imported by its prior path. A `pub use` may have been removed, or the enum itself may have been renamed or removed entirely.
        ref: https://doc.rust-lang.org/cargo/reference/semver.html#item-remove
       impl: https://github.com/obi1kenobi/cargo-semver-checks/tree/v0.50.0/src/lints/enum_missing.ron

Failed in:
  enum litebox_broker_core::fs::FileType, previously in file /home/runner/work/litebox/litebox/target/semver-checks/git-ulitebox/a813a7f2b26a346df12a5496b298b75bc3edb3c9/litebox_broker_core/src/fs/mod.rs:79

--- failure auto_trait_impl_removed: auto trait no longer implemented ---

Description:
A public type has stopped implementing one or more auto traits. This can break downstream code that depends on the traits being implemented.
        ref: https://doc.rust-lang.org/reference/special-types-and-traits.html#auto-traits
       impl: https://github.com/obi1kenobi/cargo-semver-checks/tree/v0.50.0/src/lints/auto_trait_impl_removed.ron

Failed in:
  type BrokerCoreBuilder is no longer UnwindSafe, in /home/runner/work/litebox/litebox/litebox_broker_userland/src/builder.rs:77
  type BrokerCoreBuilder is no longer RefUnwindSafe, in /home/runner/work/litebox/litebox/litebox_broker_userland/src/builder.rs:77

--- failure constructible_struct_adds_field: struct exhaustively constructible through public API adds field ---

Description:
A pub struct that could be exhaustively constructed with a literal using only public API has a new pub field, breaking existing exhaustive literals.
        ref: https://doc.rust-lang.org/reference/expressions/struct-expr.html
       impl: https://github.com/obi1kenobi/cargo-semver-checks/tree/v0.50.0/src/lints/constructible_struct_adds_field.ron

Failed in:
  field CliArgs.broker_control_channel in /home/runner/work/litebox/litebox/litebox_runner_windows_on_linux_userland/src/lib.rs:45

--- failure inherent_method_missing: pub method removed or renamed ---

Description:
A publicly-visible method or associated fn is no longer available under its prior name. It may have been renamed or removed entirely.
        ref: https://doc.rust-lang.org/cargo/reference/semver.html#item-remove
       impl: https://github.com/obi1kenobi/cargo-semver-checks/tree/v0.50.0/src/lints/inherent_method_missing.ron

Failed in:
  LinuxShimBuilder::default_fs, previously in file /home/runner/work/litebox/litebox/target/semver-checks/git-ulitebox/a813a7f2b26a346df12a5496b298b75bc3edb3c9/litebox_shim_linux/src/lib.rs:228

--- failure method_parameter_count_changed: pub method parameter count changed ---

Description:
A publicly-visible method now takes a different number of parameters, not counting the receiver (self) parameter.
        ref: https://doc.rust-lang.org/cargo/reference/semver.html#fn-change-arity
       impl: https://github.com/obi1kenobi/cargo-semver-checks/tree/v0.50.0/src/lints/method_parameter_count_changed.ron

Failed in:
  litebox_shim_linux::LinuxShim::load_program takes 5 parameters in /home/runner/work/litebox/litebox/target/semver-checks/git-ulitebox/a813a7f2b26a346df12a5496b298b75bc3edb3c9/litebox_shim_linux/src/lib.rs:265, but now takes 4 parameters in /home/runner/work/litebox/litebox/litebox_shim_linux/src/lib.rs:250

--- failure inherent_method_missing: pub method removed or renamed ---

Description:
A publicly-visible method or associated fn is no longer available under its prior name. It may have been renamed or removed entirely.
        ref: https://doc.rust-lang.org/cargo/reference/semver.html#item-remove
       impl: https://github.com/obi1kenobi/cargo-semver-checks/tree/v0.50.0/src/lints/inherent_method_missing.ron

Failed in:
  WindowsShimBuilder::new, previously in file /home/runner/work/litebox/litebox/target/semver-checks/git-ulitebox/a813a7f2b26a346df12a5496b298b75bc3edb3c9/litebox_shim_windows/src/lib.rs:406
  WindowsShimBuilder::default_fs, previously in file /home/runner/work/litebox/litebox/target/semver-checks/git-ulitebox/a813a7f2b26a346df12a5496b298b75bc3edb3c9/litebox_shim_windows/src/lib.rs:423

--- failure method_parameter_count_changed: pub method parameter count changed ---

Description:
A publicly-visible method now takes a different number of parameters, not counting the receiver (self) parameter.
        ref: https://doc.rust-lang.org/cargo/reference/semver.html#fn-change-arity
       impl: https://github.com/obi1kenobi/cargo-semver-checks/tree/v0.50.0/src/lints/method_parameter_count_changed.ron

Failed in:
  litebox_shim_windows::WindowsShim::load_program takes 4 parameters in /home/runner/work/litebox/litebox/target/semver-checks/git-ulitebox/a813a7f2b26a346df12a5496b298b75bc3edb3c9/litebox_shim_windows/src/lib.rs:507, but now takes 3 parameters in /home/runner/work/litebox/litebox/litebox_shim_windows/src/lib.rs:488