chore: Skip some CI workflows for benchmark changes

[andygrove]

Which issue does this PR close?

Closes #.

Rationale for this change

It is really annoying to run Spark SQL tests and all Comet tests when modifying benchmarks.

What changes are included in this PR?

Skip PR builds and Spark SQL tests when PRs only touch benchmarks.

Add a new workflow: .github/workflows/pr_benchmark_check.yml

This lightweight workflow triggers only when benchmark files change and runs:

• cargo fmt - Rust formatting check
• cargo clippy - Rust linting
• cargo check --benches - Verify benchmarks compile
• mvnw compile test-compile - Scala compilation
• scalafix - Scala linting

How are these changes tested?

[codecov-commenter]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 59.55%. Comparing base (f09f8af) to head (6869f79).
⚠️ Report is 811 commits behind head on main.

Additional details and impacted files

@@             Coverage Diff              @@
##               main    #3030      +/-   ##
============================================
+ Coverage     56.12%   59.55%   +3.43%     
- Complexity      976     1379     +403     
============================================
  Files           119      167      +48     
  Lines         11743    15496    +3753     
  Branches       2251     2569     +318     
============================================
+ Hits           6591     9229    +2638     
- Misses         4012     4970     +958     
- Partials       1140     1297     +157     

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[comphead]

do we need pull_request? should just push be enough 🤔

[andygrove]

I'm not sure, tbh, but all of the other workflows have both push and pull_request

[comphead]

Thanks @andygrove