feat: add pyproject.toml schema

[bollwyvl]

Description

References:

• for JSON schema for pyproject.toml [tool.pixi] #1089
• some future PR that adds this to schema store, with automated future PRs

As always, thanks so much for pixi! ❤️

This starts the groundwork for improving the editing experience of [tool.pixi] in pyproject.toml.

Once published, a pyproject.toml author could (at least initially) add a comment like:

# pyproject.toml
#:schema https://pixi.sh/v0.xx.y/schema/manifest/pyproject/schema.json

...and start getting interactive features like completion, signature display, validation, etc.

Future work (likely not by maigc CI token-averse me) could automate updating the partial-pixi.json to schemastore on release, such that even without a comment or $schema, completing .ptab would start offering up-to-date pixi options. Of course, #2748 would help the next step a lot! 😜

Changes:

• pixi.toml
  • use jsonschema-rs, relock

    • this was easier than wrangling types-jsonschema, and is faster/has no dependencies

• schema/
  • model.py
    • generate pyproject/schema.json
    • generate pyproject/partial-pixi.json as per other tools on schemastore
  • test_manifest.py
    • add type hints, remove typechecker magic comments
    • test all discovered ../**/**/pyproject.toml with the full and partial schema
    • add a couple examples (happened to pick choices)
  • docs_hooks.py
    • deploy to site/schema/manifest/pyproject/

How Has This Been Tested?

• put all existing pyproject.toml under test in test_manifest.py
• add a few valid and invalid fixtures

Checklist:

• I have performed a self-review of my own code
• I have commented my code, particularly in hard-to-understand areas
• I have made corresponding changes to the documentation
• I have added sufficient tests to cover my changes.
• I have verified that changes that would impact the JSON schema have been made in schema/model.py.