Utilizing `uv` workspaces

[dangotbanned]

Adapted from (#881 (comment))

Description

(#3631) migrated us to an src/ layout and (#3608) is migrating us from uv pip to uv sync.
uv workspaces are a feature that we can start to benefit from, so this issue is just collecting ideas for how we might do that.

Important

None of this needs to be part of (#3608), beyond the test-plugin change that's already there

Use-cases

• https://github.com/narwhals-dev/narwhals-daft
  • And generally any future plugins
• feat: Introduce testing.constructors module and a pytest plugin #3552
• chore: move tests to a narwhals-testing package #3475
• tpch
  • Interestingly, it was a package before and was last updated the same day [Enh]: consider switching to src layout #881 opened

Related

• https://github.com/j178/prek
  • https://github.com/j178/prek#who-is-using-prek
  • https://prek.j178.dev/workspace/
  • hi j178/prek#73 (comment)
  • chore: Adopt uv as package manager #3608 (comment)
  • chore: Adopt uv as package manager #3608 (comment)
• https://tombi-toml.github.io/tombi/docs/extensions/tombi-extension-pyproject
  • chore: Adopt uv as package manager #3608 (comment)

[FBruzzesi]

@dangotbanned if you want to start somewhere, I pushed te migration of tpch to a workspace in a branch (chore/tpch-to-workspace). It's work in progress but a good (?) start