autoimport: track and close SQLite connections across worker threads

[mcepl]

AutoImport dynamically allocates per-thread SQLite connections using threading.local(). However, AutoImport.close() only closed the connection belonging to the calling thread, orphaning any connections created by worker threads and triggering ResourceWarning on Python 3.12+.

Keep a thread-safe registry of all active connections on the AutoImport instance, create connections with check_same_thread=False, and ensure AutoImport.close() commits and closes all registered connections. Also expose close_thread_connection() for worker threads and implement context manager protocol support on AutoImport.

Fixes: #886

Checklist (delete if not relevant):

• I have added tests that prove my fix is effective or that my feature works
• I have updated CHANGELOG.md
• I have made corresponding changes to user documentation for new features
• I have made corresponding changes to library documentation for API changes

[codecov]

Codecov Report

❌ Patch coverage is 95.31250% with 6 lines in your changes missing coverage. Please review.
✅ Project coverage is 95.33%. Comparing base (2bd17a8) to head (411c697).

Files with missing lines	Patch %	Lines
rope/contrib/autoimport/sqlite.py	90.00%	6 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           master     #889      +/-   ##
==========================================
- Coverage   95.34%   95.33%   -0.01%     
==========================================
  Files         134      134              
  Lines       26819    26922     +103     
==========================================
+ Hits        25570    25667      +97     
- Misses       1249     1255       +6     

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