deprecate exception classes in Cursor attributes

[methane]

No description provided.

[Copilot]

Pull request overview

This PR deprecates accessing DB-API exception classes via Cursor attributes by replacing the existing cursor-level exception attributes with a BaseCursor.__getattr__ fallback that emits a DeprecationWarning and forwards lookups to the underlying exceptions module.

Changes:

• Remove cursor-level exception attributes previously defined on BaseCursor.
• Add BaseCursor.__getattr__ to intercept exception attribute access and emit a deprecation warning.
• Forward exception attribute lookups to MySQLdb._exceptions.

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[codecov]

Codecov Report

❌ Patch coverage is 25.00000% with 6 lines in your changes missing coverage. Please review.
✅ Project coverage is 88.75%. Comparing base (e2a908b) to head (11dc0c9).
⚠️ Report is 37 commits behind head on main.

Files with missing lines	Patch %	Lines
src/MySQLdb/cursors.py	14.28%	6 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #782      +/-   ##
==========================================
- Coverage   88.86%   88.75%   -0.12%     
==========================================
  Files           7        7              
  Lines         548      560      +12     
==========================================
+ Hits          487      497      +10     
- Misses         61       63       +2     

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