Replace `pip` with `uv pip`

[callumforrester]

For the devcontainer: We should use uv pip instead of pip because it is faster.

Acceptance Criteria

• Devcontainer build installs dependencies using uv pip instead of pip
• uv pip is aliased to pip for backwards-compatibility (or we agree to do a breaking change)
• Devcontainer build is manually tested
• Devcontainer build is timed compared to main

[coretl]

astral-sh/uv#12197 seems relevant

[callumforrester]

@coretl Presume you need to do a bootstap install of pip install uv or something?

[coretl]

If we base on ghcr.io/astral-sh/uv:python3.11-bookworm instead of python:3.11 then it's already there.

Or one of the other options in https://docs.astral.sh/uv/guides/integration/docker/#available-images