Do not swallow non-TypeError exceptions in feature-detection fallbacks

[devdanzin]

What do these changes do?

Several feature-detection fallbacks cleared every pending exception when a fallback path was taken:
view richcompare and items-view __contains__ measuring len(other), items-view __contains__
computing the identity, MultiDict.__eq__ probing keys(), and extend()/constructor probing
items(). A MemoryError or KeyboardInterrupt raised by the user object was silently discarded. Each
is now guarded with PyErr_ExceptionMatches() so only the expected TypeError/AttributeError is
cleared and anything else propagates — the same pattern the sibling sites in views.h already use.
C-extension-only; the pure-Python backend propagates naturally.

Are there changes in behavior for the user?

Yes (edge case): an exception other than TypeError/AttributeError (notably MemoryError,
KeyboardInterrupt) raised by an object being probed now propagates instead of being swallowed. The
normal fallbacks (a non-sized or non-mapping object) are unchanged.

Is it a substantial burden for the maintainers to support this?

No. It applies the module's existing guard pattern to the few sites that missed it.

Related issue number

Findings from the C-extension analysis report #1306.

Checklist

• I think the code is well written
• Unit tests for the changes exist (test_non_typeerror_exceptions_are_not_swallowed)
• Documentation reflects the changes (no public API change)
• N/A — no CONTRIBUTORS.txt in this repo
• Add a new news fragment into the CHANGES/ folder

[codspeed-hq]

Merging this PR will not alter performance

✅ 242 untouched benchmarks

---

_{Comparing devdanzin:fix/broad-pyerr-clear (e5d1910) with master (e71a593)}

[codecov]

Codecov Report

❌ Patch coverage is 90.00000% with 2 lines in your changes missing coverage. Please review.
✅ Project coverage is 99.80%. Comparing base (e71a593) to head (e5d1910).

Files with missing lines	Patch %	Lines
tests/test_multidict.py	90.00%	2 Missing ⚠️

❌ Your patch check has failed because the patch coverage (90.00%) is below the target coverage (95.00%). You can increase the patch coverage or adjust the target coverage.
❌ Your project check has failed because the head coverage (99.92%) is below the target coverage (100.00%). You can increase the head coverage or adjust the target coverage.

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #1382      +/-   ##
==========================================
- Coverage   99.86%   99.80%   -0.06%     
==========================================
  Files          28       28              
  Lines        3627     3647      +20     
  Branches      265      265              
==========================================
+ Hits         3622     3640      +18     
- Misses          3        5       +2     
  Partials        2        2              

Flag	Coverage Δ
CI-GHA	99.80% <90.00%> (-0.06%)	⬇️
pytest	99.80% <90.00%> (-0.06%)	⬇️

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