fix(backends): serialize timedelta values in JSON responses

[aiolibsbot]

What: Serialize datetime.timedelta values in JSON responses so resources with sa.Interval columns can be read.

Why: sa.Interval columns yield timedelta, which Encoder.default didn't handle (it covered date/time/Enum/bytes/Decimal/UUID). Any read of a resource with an Interval column raised TypeError and returned a 500. Interval isn't in FIELD_TYPES, so it falls through to the default TextField/TextInput — setup succeeds, but the first read crashes.

How: Added timedelta to the existing isinstance(o, (date, time)) → str(o) branch, matching the TextField the column renders as. This closes the last known unhandled value type from the sqlalchemy.py TODO block, continuing the Encoder/FIELD_TYPES drift fixes (Decimal #1172, UUID #1173).

Testing: Added test_interval — an end-to-end read of an sa.Interval column, asserting the response serializes ("2:30:00") rather than 500ing. Full backends suite: 19 passed.

---

Quality Report

Changes: 2 files changed, 40 insertions(+), 3 deletions(-)

Code scan: clean

Tests: failed (command not found)

Branch hygiene: clean

Generated by Kōan

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 95.63%. Comparing base (2448fd1) to head (93d037b).
⚠️ Report is 168 commits behind head on master.

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #1174      +/-   ##
==========================================
+ Coverage   95.56%   95.63%   +0.06%     
==========================================
  Files          21       21              
  Lines        2954     2975      +21     
  Branches      193      199       +6     
==========================================
+ Hits         2823     2845      +22     
+ Misses        105      104       -1     
  Partials       26       26              

Flag	Coverage Δ
integration	81.22% <100.00%> (+0.27%)	⬆️
js	83.89% <ø> (ø)
unit	97.48% <100.00%> (+0.06%)	⬆️

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