Spike: Investigate using `uv` to manage envtire project

[callumforrester]

#245 is an easy win, we would like to make further use of uv. Python projects have always required a slightly awkward bringing together of many tools from many vendors, one well-written tool that can manage the venv, tasks and dependencies would be very useful.

For tasks (i.e. a replacement for tox) there is an outstanding issue upstream: astral-sh/uv#5903

@coretl to comment on the issues/unknowns that need to be investigated.

Acceptance Criteria

• A reasonable set of instructions for moving to uv is produced

[coretl]

Starting place is https://docs.astral.sh/uv/guides/integration/fastapi/

Integration with devcontainer is essentially following https://docs.astral.sh/uv/guides/integration/docker/ and putting the contents in devcontainer.

However I don't like their idea anonymous mount .venv. You can specify a different venv location with UV_PROJECT_ENVIRONMENT so we could set that to /venv and leave it where it is at the moment.

[callumforrester]

I agree with using ${UV_PROJECT_ENVIRONMENT}! How many breaking changes do we think are needed here?

[coretl]

Not sure until this is tried, hopefully not much, but it adds a lockfile so we need to write docs around managing that...

[OCopping]

I have already looked into using uv in phoebus-guibuilder (soon to be techui-builder).

This is using hatch as the runner replacement until uv adds its own.
I have also implemented the CI with this.

[callumforrester]

Interesting! Don't suppose you want to turn it into a PR to the template?