Add local QA helpers and python 3.13/trixie support

[dannystaple]

• Add a docker testing images - for python 3.9, 3.10, 3.11 and 3.13 in trixie.
• Fix test mocking issue in tox.ini. Tests and functionality unchanged.
• Add a LOCAL_QA.md guide, showing how to run these checks within the docker env.
• Minor fix to checks - exporting the TERM settings.

This is a port of pimoroni/inventorhatmini-python#16 to the boilerplate.

A couple of whys

• Why dockerfile? Because on a desktop, I don't have GitHub's setup python, and this would be a reasonable way to get to the matrix of versions. Plus it's got the other bits it needs (presuming I haven't missed some, we'll find out).
• Why uv - managing a python setup with lockfiles means fewer package update surprises. It does need to be relocked sometimes though.
• Why a lockfile - so we get fewer moments of "ahhh... this is no longer compatible with todays build of smbus", at least until we relock because we meant it.
• Why a local qa doc - so people can run this stuff at desk without having to discover it all again.

Mostly Developer Experience (devx) to make fixing the ci failures a bit easier.

Testing

• Make check, make shellcheck, make qa and make pytest were ran locally on this - all pythons seem to work.
• CI Workflows for the rest of the matrix are mostly passing. 3.9 has issues - which looks like hatch support has dropped off for it.

[Copilot]

Pull request overview

Note

Copilot was unable to run its full agentic suite in this review.

Adds a Docker-based local QA environment with a pinned dependency lockfile, documentation for running checks in the container, and tweaks the existing tox and check.sh setup to better support isolated testing.

Changes:

• New Dockerfile.testing + requirements-dev.lock providing a reproducible dev/test image driven by uv.
• New LOCAL_QA.md documenting how to build and run QA targets inside the container.
• tox.ini switched to skip_install + manual pip install --no-deps to avoid pulling hardware-specific deps; check.sh exports TERM.

Reviewed changes

Copilot reviewed 4 out of 5 changed files in this pull request and generated 5 comments.

Show a summary per file

File	Description
Dockerfile.testing	New image: uv + Python 3.11, system tools, non-root appuser, installs from lockfile.
requirements-dev.lock	New uv-generated lockfile pinning all dev deps for Python 3.11.
LOCAL_QA.md	New docs describing build/run commands and lockfile regeneration.
tox.ini	Skips install and instead does pip install --no-deps in commands_pre; also skip_install for qa.
check.sh	Exports TERM so subprocesses inherit the value.

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[Gadgetoid]

Whew, thank you, might take me a while to get to this since I'm buried in Pico stuff at the moment. I also really ought to play with uv more.