fix: correct race condition in with_for_update

[cofin]

This corrects an issue in the with_for_update behavior:

• Before the change, passing with_for_update to service.update() or repository.update() only affected the post-flush session.refresh() call. The row that gets copied and mutated was always retrieved with a plain SELECT, so two concurrent writers could both read the same version
  • Now the with_for_update flag is honored when the row is first fetched (both in the service’s item_id branch and inside SQLAlchemyAsyncRepository.get()). When you call service.update(..., with_for_update=True) (or pass the richer dict form/ForUpdateArg), the initial SELECT ... FOR UPDATE runs, so the session holds the expected lock before any field copying or merges occur.

[codecov-commenter]

Codecov Report

❌ Patch coverage is 73.33333% with 8 lines in your changes missing coverage. Please review.
✅ Project coverage is 80.35%. Comparing base (c08ef25) to head (0ab0faf).

Files with missing lines	Patch %	Lines
advanced_alchemy/repository/_async.py	73.33%	2 Missing and 2 partials ⚠️
advanced_alchemy/repository/_sync.py	73.33%	2 Missing and 2 partials ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #607      +/-   ##
==========================================
+ Coverage   80.32%   80.35%   +0.02%     
==========================================
  Files          87       87              
  Lines        6405     6433      +28     
  Branches      828      838      +10     
==========================================
+ Hits         5145     5169      +24     
  Misses       1000     1000              
- Partials      260      264       +4     

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[sonarqubecloud]

Quality Gate passed

Issues
0 New issues
0 Accepted issues

Measures
0 Security Hotspots
84.0% Coverage on New Code
0.0% Duplication on New Code

See analysis details on SonarQube Cloud

[github-actions]

Documentation preview will be available shortly at https://litestar-org.github.io/advanced-alchemy-docs-preview/607