Repair the public CSS arrival interval matcher

[wangyinz]

Fixes #832

Repairs the public CSS arrival interval matcher contracts, including inclusive MongoDB bounds, deterministic nearest-arrival selection, collection configuration, and error logging. Adds focused real-Mongo regression coverage for boundary, multi-match, missing-field, and custom-collection behavior.

Renewed resource-lifecycle review

The first version materialized a PyMongo cursor for multi-match selection but returned or raised without closing it; its list-based test double hid that leak. Commit a38586dd wraps the complete multi-match selection in try/finally, closes the cursor on success and failure, and adds a real cursor-like test double that proves both paths. It does not change the arrival-selection formula or error policy.

Validation: focused contract 14 passed, 1 skipped (the only skip was the absent local MongoDB service); Black 26.5.1, Python 3.12/3.13 py_compile, and git diff --check passed.

This PR intentionally remains draft pending human data/API review.

[codecov]

Codecov Report

❌ Patch coverage is 92.30769% with 2 lines in your changes missing coverage. Please review.
✅ Project coverage is 68.65%. Comparing base (61b06b9) to head (a38586d).

Files with missing lines	Patch %	Lines
python/mspasspy/db/matcher.py	92.30%	2 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           master     #975      +/-   ##
==========================================
+ Coverage   68.35%   68.65%   +0.30%     
==========================================
  Files         173      173              
  Lines       34397    34402       +5     
  Branches     2474     2474              
==========================================
+ Hits        23511    23620     +109     
+ Misses      10002     9898     -104     
  Partials      884      884              

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