Add a catch-all error handler using ProblemDetails

[rwb27]

This may not make it out of draft - it was intended to reduce the ASGI noise in the logs, but it doesn't do that: a stack trace still gets logged to the uvicorn log, and nothing elsewhere.

[barecheck]

Barecheck - Code coverage report

Total: 97.25%

Your code coverage diff: -0.06% ▾

Uncovered files and lines

File	Lines
src/labthings_fastapi/server/__init__.py	261-262, 277, 281, 337, 351-354