[Python] Merge runtime type-check wrappers

[Mazen050]

Summary

Fixes #20226

This PR reduces runtime type-checking overhead in the Python SDK by consolidating two nested DoFn wrappers into a single RuntimeTypeCheckWrapperDoFn.

Previously, input and output checks were handled by separate wrappers. The merged wrapper aims to preserve existing type-checking behavior while eliminating one level of Python call indirection per processed element.

Changes

• Consolidate OutputCheckWrapperDoFn and TypeCheckWrapperDoFn into RuntimeTypeCheckWrapperDoFn.
• Cache the unbound process function while avoiding storing a bound method on the wrapper, preserving stateful DoFn validation.
• Preserve input and output type checking, output-shape validation, and transform error labeling.
• Add regression tests for wrapper application, error reporting, result preservation, and stateful DoFn compatibility.

Tests

• apache_beam/typehints/typecheck_test.py: 18 passed.
• apache_beam/transforms/ptransform_test.py: 202 passed, 4 skipped.

Performance

Compared the original and modified implementations using Beam's existing runtime_type_check_microbenchmark.

Configuration: 20 DoFns and three timing repetitions per configuration.

Elements	Simple types (before → after)	Nested types (before → after)
501	3.22s → 3.06s	3.90s → 3.41s
1,001	5.44s → 5.39s	6.44s → 6.07s
1,501	7.57s → 7.39s	8.93s → 8.83s
2,001	9.91s → 9.46s	11.84s → 11.22s

At 2,001 elements, the measured runtime was approximately 4.5% lower for simple type hints and 5.2% lower for nested type hints in this local run.

These measurements are preliminary and may vary by environment. They demonstrate the results of this benchmark configuration, not a guaranteed improvement for all pipelines.

[github-actions]

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[codecov]

Codecov Report

❌ Patch coverage is 94.11765% with 2 lines in your changes missing coverage. Please review.
✅ Project coverage is 56.23%. Comparing base (76f6e6d) to head (6190609).
⚠️ Report is 139 commits behind head on master.

Files with missing lines	Patch %	Lines
sdks/python/apache_beam/typehints/typecheck.py	94.11%	2 Missing ⚠️

Additional details and impacted files

@@             Coverage Diff              @@
##             master   #40501      +/-   ##
============================================
+ Coverage     56.16%   56.23%   +0.06%     
  Complexity     2288     2288              
============================================
  Files          1124     1124              
  Lines        178336   178366      +30     
  Branches       1489     1489              
============================================
+ Hits         100170   100303     +133     
+ Misses        75645    75542     -103     
  Partials       2521     2521              

Flag	Coverage Δ
python	79.68% <94.11%> (+0.13%)	⬆️

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