fix: encode composite PKs in bulk responses

[8dazo]

Summary

• updateMany / deleteMany now return full pipe-joined IDs for composite primary keys ("1|2"), matching getList / getOne / getMany.
• SQLAlchemy bulk methods return every RETURNING PK column instead of scalars() (first column only).
• _convert_ids uses the same "|".join(...) encoding as _convert_record.
• Adds test_composite_pk_api covering list, get, update, bulk update, and bulk delete.

Fixes #1192

Test plan

• pytest tests/test_backends_sqlalchemy.py::test_composite_pk_api
• Single-PK bulk tests still pass (test_update_many, test_delete_many)
• CI green on this PR

Made with Cursor

[greptile-apps]

Confidence Score: 5/5

The PR appears safe to merge.

No blocking failure remains.

_{Reviews (2): Last reviewed commit: "fix: avoid ReturningDelete reassignment ..." | Re-trigger Greptile}

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 95.85%. Comparing base (ef6fc55) to head (f2bf2f7).
⚠️ Report is 6 commits behind head on master.

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #1193      +/-   ##
==========================================
+ Coverage   95.76%   95.85%   +0.08%     
==========================================
  Files          21       21              
  Lines        2955     3014      +59     
  Branches      193      200       +7     
==========================================
+ Hits         2830     2889      +59     
  Misses        100      100              
  Partials       25       25              

Flag	Coverage Δ
integration	81.24% <50.00%> (-0.42%)	⬇️
js	83.96% <ø> (ø)
unit	97.64% <100.00%> (+0.13%)	⬆️

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