fix(#648): restore psycopg autocommit after transactions

[cofin]

Summary

• track SQLSpec transaction ownership separately from libpq transaction status
• restore the connection's original autocommit mode after successful commit or rollback
• preserve transaction state when native completion fails and report autocommit restoration failures separately
• keep inherited Cockroach retry and statement-stack paths from taking ownership of implicit psycopg transactions

Fixes #648.

[codecov-commenter]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 77.07%. Comparing base (ed4ed5f) to head (cd8742e).

Additional details and impacted files

@@           Coverage Diff            @@
##             main     #652    +/-   ##
========================================
  Coverage   77.06%   77.07%            
========================================
  Files         475      475            
  Lines       67212    67252    +40     
  Branches    10075     9182   -893     
========================================
+ Hits        51800    51832    +32     
- Misses      12017    12024     +7     
- Partials     3395     3396     +1     

Flag	Coverage Δ
integration	60.68% <86.95%> (+0.01%)	⬆️
py3.10	75.36% <100.00%> (+0.01%)	⬆️
py3.11	75.37% <100.00%> (+0.01%)	⬆️
py3.12	75.37% <100.00%> (+0.01%)	⬆️
py3.13	75.37% <100.00%> (+0.01%)	⬆️
py3.14	76.25% <100.00%> (+<0.01%)	⬆️
unit	64.44% <100.00%> (+0.02%)	⬆️

Flags with carried forward coverage won't be shown. Click here to find out more.

Files with missing lines	Coverage Δ
sqlspec/adapters/psycopg/driver.py	83.67% <100.00%> (+1.20%)	⬆️

... and 2 files with indirect coverage changes

🚀 New features to boost your workflow:

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