fix: Python 3.10 compat — timezone.utc + onnxruntime 1.23.2 (unbreaks prod)

[schutera]

What

from datetime import UTC / datetime.now(UTC) in both
duckdb-service/services/log_ring.py and image-service/services/log_ring.py
requires Python 3.11+ — the UTC alias was only added to datetime in 3.11.

Why it matters

The production host runs Python 3.10. Deploying aac9c78 (current main)
crashed both python services at import time: log_ring.install() runs at
import in app.py, so the ImportError takes the service down before it serves
any traffic. Prod has been held on the prior known-good revision until this lands.

Fix

Replace UTC with the equivalent timezone.utc (available since 3.2). Behavior
is identical on 3.11+ and now works on 3.10:

• _now_iso() → millisecond ISO string with a Z suffix
• log-rotation filename stamp %Y-%m-%d_%H-%M-%S

Both copies of log_ring.py are kept byte-identical.

Verification (run on Python 3.10.12, same minor as prod)

• ✅ py_compile of both files
• ✅ full compileall sweep of every python service/tooling dir — no other
  3.11-only syntax anywhere
• ✅ grepped origin/main for other 3.11-isms (tomllib, StrEnum,
  ExceptionGroup, except*, asyncio.TaskGroup, typing.Self,
  datetime.UTC) — none outside these two files
• ✅ stamp output confirmed byte-identical to the old UTC form
• fromisoformat call sites (measurements.py, weather_worker.py) already
  guard for pre-3.11 input — left as-is

Also in this PR: onnxruntime pinned for Python 3.10

image-service/requirements.txt pinned onnxruntime==1.27.0, which has no
cp310 wheel (pip offers max 1.23.2 on Python 3.10) — so installing
image-service's requirements would fail on the 3.10 prod host. This PR pins it to
onnxruntime==1.23.2 (the highest cp310 wheel), verified to load and run the
exported hole_detector.onnx on Python 3.10.12. Bump back up once the host moves
to Python 3.11+. Server-side inference only — the ESP runs no models
(ADR-028).

Introduced in 8938899 (part of #180, which closed #178).

🤖 Generated with Claude Code

[cofade]

Closing as fully superseded by #195 (merged to main as a0e7374). Rebasing this branch onto current main leaves zero diff — both commits evaporate:

• timezone.utc fix (both log_ring.py copies) — git drops it automatically on rebase: patch contents already upstream. ci: test the Python services across a 3.10–3.14 matrix (closes #192) #195 carried the byte-identical from datetime import UTC → timezone.utc change into both files.
• onnxruntime pin — superseded by a more general fix. This PR hard-pinned onnxruntime==1.23.2 / numpy==1.26.4 to keep the Python-3.10 prod host installable. ci: test the Python services across a 3.10–3.14 matrix (closes #192) #195 instead floated them to onnxruntime>=1.23.2 / numpy>=2.0.0 (ADR-029) so each cell of the new 3.10–3.14 CI matrix resolves a per-interpreter wheel. A hard ==1.23.2 would now break the 3.14 cell (no cp314 wheel; cp314 needs ≥ 1.24.1), and numpy==1.26.4 has no cp314 wheel either. The 3.10 host still resolves onnxruntime 1.23.2 from the floated lower bound, so prod stays installable — this PR's intent is preserved and generalized.

Verified: git diff origin/main..HEAD after rebase is empty. Nothing left to merge.

Follow-up that outlives this PR: the host should still bump to Python 3.11+ eventually, and the repo's runtime version is specified three different ways (container 3.12-slim, deploy docs 3.11, the crashed host 3.10) — reconciling that to one authoritative version is tracked separately from #192/#195.