fix(backends): serialize UUID values in JSON responses

[aiolibsbot]

What: Serialize uuid.UUID values in JSON API responses.

Why: sa.Uuid columns are mapped to TextField/TextInput in FIELD_TYPES, but the value SQLAlchemy returns is a uuid.UUID object. Encoder.default in backends/abc.py handled date/time/Enum/bytes but not UUID, so json.dumps raised TypeError and every read (get_one/get_list/get_many) of a resource with a UUID column returned 500. Same class of gap as the Decimal fix (#1172); UUID was the next unhandled type.

How: One branch in Encoder.default: UUID -> str(o) (canonical form). This matches the TextField/TextInput contract and the canonical-form regex validator already emitted for UUID inputs (#1168).

Testing: Added test_uuid — an end-to-end get_one against a model with a Mapped[uuid.UUID] column, asserting 200 and the canonical string in the payload. Full suite: 99 passed, 1 xfailed.

---

Quality Report

Changes: 2 files changed, 43 insertions(+)

Code scan: clean

Tests: failed (command not found)

Branch hygiene: clean

Generated by Kōan

[codecov]

Codecov Report

❌ Patch coverage is 96.00000% with 1 line in your changes missing coverage. Please review.
✅ Project coverage is 95.66%. Comparing base (2448fd1) to head (d0fb38c).
⚠️ Report is 168 commits behind head on master.

Files with missing lines	Patch %	Lines
aiohttp_admin/backends/abc.py	66.66%	0 Missing and 1 partial ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #1173      +/-   ##
==========================================
+ Coverage   95.56%   95.66%   +0.10%     
==========================================
  Files          21       21              
  Lines        2954     2979      +25     
  Branches      193      200       +7     
==========================================
+ Hits         2823     2850      +27     
+ Misses        105      103       -2     
  Partials       26       26              

Flag	Coverage Δ
integration	80.92% <33.33%> (-0.03%)	⬇️
js	83.89% <ø> (ø)
unit	97.52% <96.00%> (+0.10%)	⬆️

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