MAINT: Enforce PLW2901 (avoid loop/context var overwrite)

[dev-KingMaster]

Summary

• Removes PLW2901 ignore and fixes all instances where loop or context-manager variables were overwritten, improving readability and avoiding subtle bugs.
• Why: Aligns with Ruff “no var overwrite” guidance; safer, clearer code; progresses Cleanup ruff ignores #3327.
• Scope: Touches core modules (e.g., pypdf/_cmap.py, _doc_common.py, _page.py, _writer.py, _text_extraction/_layout_mode/_font.py, filters.py, generic/_files.py) and a few tests where the pattern occurred.
• Approach: Introduces new local names (*_obj, *_val, operands_for_tm, etc.) instead of reassigning loop/context variables; no behavioral changes.
• Config: Removes "PLW2901" from [tool.ruff.lint].ignore in pyproject.toml.
• Validation: ruff check passes cleanly with PLW2901 enforced. No functional logic altered; tests adjusted only for variable naming where needed.

Contribution by Gittensor, learn more at https://gittensor.io/

[codecov]

Codecov Report

❌ Patch coverage is 98.38710% with 1 line in your changes missing coverage. Please review.
✅ Project coverage is 97.10%. Comparing base (3b5c85f) to head (e385405).

Files with missing lines	Patch %	Lines
pypdf/_doc_common.py	92.30%	0 Missing and 1 partial ⚠️

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #3513   +/-   ##
=======================================
  Coverage   97.10%   97.10%           
=======================================
  Files          57       57           
  Lines        9711     9718    +7     
  Branches     1759     1759           
=======================================
+ Hits         9430     9437    +7     
  Misses        168      168           
  Partials      113      113           

☔ View full report in Codecov by Sentry.
📢 Have feedback on the report? Share it here.

🚀 New features to boost your workflow:

• ❄️ Test Analytics: Detect flaky tests, report on failures, and find test suite problems.

[stefan6419846]

Thanks for the PR. I have left some remarks for specific changes and some general ones.

[dev-KingMaster]

Hi @stefan6419846 I addressed all the comments.