Operation runtime hardening

[343dev]

This PR adds a shared runtime for image operations and removes invocation state from global modules.

Optimization and conversion now use the same execution flow. Each invocation owns its options, lifecycle, reporting, and signal handlers.

User-visible changes

• Optimizt selects the lossless JPEG resource limit from detected image data, not the file extension.
• Renamed JPEG files now use Guetzli’s single-operation limit.
• An interruption stops queued work and terminates active encoders when cancellation is available.
• The interruption summary reports completed operations separately.
• Abandoned operations do not appear as skipped or failed.
• Guetzli errors preserve up to 64 KiB of encoder output.
• Guetzli errors distinguish startup failures, input write failures, exit codes, and termination signals.
• One failed image operation does not stop independent operations.

Implementation

• Add a shared runtime for concurrency, resource limits, outcomes, and interruption checks.
• Use the shared runtime for optimization and conversion.
• Replace global options and lifecycle state with invocation-specific objects.
• Consolidate progress output, failure details, and summaries in one reporter.
• Remove the old global program options and summary modules.
• Add tests for runtime behavior, invocation isolation, Guetzli errors, and interruption reporting.

Breaking change

The internal execution contract now requires invocation-specific options, lifecycle, and reporting objects.