perf: push left filters through ASOF joins

[Xuanwo]

Which issue does this PR close?

• Part of ASOF join support / Specialize Range Joins #318.
• Umbrella PR: feat: support ASOF joins #23738.
• Depends on feat: add ASOF join logical semantics #23829.

Rationale for this change

An ASOF join emits each left row exactly once and does not change left-side
values. A deterministic predicate that references only the left input can
therefore run before matching. Right-only and mixed predicates must remain
above the join because unmatched right fields are NULL-padded, and volatile
predicates must keep their original evaluation point.

Pushing the safe subset reduces the number of rows entering the ASOF join
without changing query results.

GitHub shows the cumulative stack because fork branches cannot be selected as
upstream PR bases. The isolated diff for this layer is:
Xuanwo/datafusion@xuanwo/asof-logical...xuanwo/asof-filter-pushdown

What changes are included in this PR?

• Push deterministic left-only conjuncts below logical ASOF joins.
• Keep right-only, mixed, and volatile predicates above the join.
• Document the cardinality and NULL-padding assumptions at the optimizer rule.
• Add focused optimizer snapshots for all four predicate categories.

Are these changes tested?

• cargo fmt --all
• cargo clippy --all-targets --all-features -- -D warnings
• cargo test --profile ci -p datafusion-optimizer asof_join_ --all-features
• The extended workspace test command from the contributor guide

Are there any user-facing changes?

No result semantics or public APIs change. Eligible ASOF joins may execute with
fewer left-side rows after logical optimization.

[github-actions]

Thank you for opening this pull request!

Reviewer note: cargo-semver-checks reported the current version number is not SemVer-compatible with the changes in this pull request (compared against the base branch).

Details

     Cloning apache/main
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--- failure enum_variant_added: enum variant added on exhaustive enum ---

Description:
A publicly-visible enum without #[non_exhaustive] has a new variant.
        ref: https://doc.rust-lang.org/cargo/reference/semver.html#enum-variant-new
       impl: https://github.com/obi1kenobi/cargo-semver-checks/tree/v0.50.0/src/lints/enum_variant_added.ron

Failed in:
  variant LogicalPlan:AsOfJoin in /home/runner/work/datafusion/datafusion/datafusion/expr/src/logical_plan/plan.rs:301
  variant LogicalPlan:AsOfJoin in /home/runner/work/datafusion/datafusion/datafusion/expr/src/logical_plan/plan.rs:301

     Summary semver requires new major version: 1 major and 0 minor checks failed
    Finished [  60.464s] datafusion-expr
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    Building datafusion-substrait v55.0.0 (baseline)
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     Parsing datafusion-substrait v55.0.0 (baseline)
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    Checking datafusion-substrait v55.0.0 -> v55.0.0 (no change; assume patch)
     Checked [   0.331s] 223 checks: 223 pass, 31 skip
     Summary no semver update required
    Finished [ 595.250s] datafusion-substrait

[codecov-commenter]

Codecov Report

❌ Patch coverage is 44.95614% with 251 lines in your changes missing coverage. Please review.
✅ Project coverage is 81.48%. Comparing base (c4910e0) to head (3a5e377).
⚠️ Report is 20 commits behind head on main.

Files with missing lines	Patch %	Lines
datafusion/expr/src/logical_plan/plan.rs	50.25%	81 Missing and 16 partials ⚠️
datafusion/core/src/physical_planner.rs	0.00%	41 Missing ⚠️
datafusion/expr/src/logical_plan/tree_node.rs	9.30%	38 Missing and 1 partial ⚠️
datafusion/optimizer/src/analyzer/type_coercion.rs	0.00%	28 Missing ⚠️
datafusion/expr/src/logical_plan/builder.rs	60.71%	17 Missing and 5 partials ⚠️
datafusion/optimizer/src/push_down_filter.rs	84.41%	5 Missing and 7 partials ⚠️
datafusion/expr/src/logical_plan/display.rs	0.00%	10 Missing ⚠️
datafusion/optimizer/src/optimizer.rs	50.00%	0 Missing and 2 partials ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main   #24801      +/-   ##
==========================================
+ Coverage   81.47%   81.48%   +0.01%     
==========================================
  Files        1122     1123       +1     
  Lines      403629   406555    +2926     
  Branches   403629   406555    +2926     
==========================================
+ Hits       328866   331301    +2435     
- Misses      55510    55856     +346     
- Partials    19253    19398     +145     

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