fix: add was_attribute_set() guard to relationship loop in update()

[sohbit]

Description

Partial updates using model instances (e.g. Model(id=..., name='new')) were silently clearing relationships because SQLAlchemy auto-initializes unset relationship attributes to None/[], which then passed the 'is not MISSING' check and got written through to the DB.

This adds the same was_attribute_set() guard that already protects the column loop to the relationship loop, so only explicitly set relationships are copied during update().

Closes

• Bug: update() missing was_attribute_set() guard on relationship loop which silently clears relationships during partial updates #684

[sohbit]

Hi @cofin,

let me know if I can do anything in order to fix the CI here. Seems to be unrelated to the changes from the PR. Tests were passing locally.

[cofin]

@sohbit it may be a transient error. I've triggered a retry and will keep an eye on it.

[codecov-commenter]

Codecov Report

❌ Patch coverage is 50.00000% with 2 lines in your changes missing coverage. Please review.
✅ Project coverage is 80.67%. Comparing base (c98a33e) to head (f44f439).
⚠️ Report is 17 commits behind head on main.

Files with missing lines	Patch %	Lines
advanced_alchemy/repository/_sync.py	0.00%	2 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #685      +/-   ##
==========================================
- Coverage   80.69%   80.67%   -0.02%     
==========================================
  Files          99       99              
  Lines        8173     8177       +4     
  Branches     1119     1121       +2     
==========================================
+ Hits         6595     6597       +2     
- Misses       1247     1249       +2     
  Partials      331      331              

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[cofin]

LGTM