feat: load tool(s) via URL

[henryiii]

This adds --tool <name>=<url>#<pointer> support. I've also added basic support for pyodide (untested, probably can add eventually), since loading URLs is different there.

[abravalheri]

Thank you very much for working on this @henryiii.

I wonder if it would make more sense for the API layer to be more focused on complex types instead of primitives and let the CLI layer to do the lifting.

For example, would some of the following alternatives work as Python API?

Validator(
    load_tools={
       "cibuildwheel": "https://json.schemastore.org/cibuildwheel.json#/properties/tool/properties/cibuildwheel",
    }
)

# OR

Validator(
    tools=[
        RemotePlugin("cibuildwheel", "https://json.schemastore.org/cibuildwheel.json#/properties/tool/properties/cibuildwheel"),
        # Would require `RemotePlugin.load()` or something similar
    ]
)

# OR

Validator(
    plugins=[
        PluginWrapper(...),
        RemotePlugin("cibuildwheel", "https://json.schemastore.org/cibuildwheel.json#/properties/tool/properties/cibuildwheel"),
        # Would require `RemotePlugin.schema` to lazily trigger/cache the download
    ]
)

[henryiii]

I basically followed your third suggestion, though I didn't implement lazy loading (it would complicate the implementation quite a bit, and since id has to be loaded pretty early, I don't think there's a benefit; I did cache though). I also added a helper class method to easily handle the tool=url form since it's used multiple places.

[henryiii]

I also had to add extra_plugins, since setting a plugin replaces ALL_PLUGINS. Ideally, that would be an all_plugins: bool parameter and one plugin list. Can change the API to that if you want.

[abravalheri]

Thank you very much, @henryiii.

This looks good. If you are happy with it, please feel free to merge.

I will be away from a proper computer in December, and probably less responsive. But if at any point you want to cut a release, please feel free to do so. I believe that it can be done via the github webUI, and then the CI should take care of it...