This commit introduces support for the cog context into the Replicate
SDK. The `current_scope` helper now makes per-prediction context
available via the `current_scope().context` dict.

A cog model can then provide a REPLICATE_API_TOKEN on a per-prediction
basis to be used by the model.

    def predict(prompt: str) -> str:
        replicate = Replicate()
        output = replicate.run("anthropic/claude-3.5-haiku", {input:
{"prompt": "prompt"}})
        return output

Co-authored-by: Philip Potter <philip.g.potter@gmail.com>

This migrates the project from using `rye` to `uv`, both tools provided
by astral.sh but the latter is deemed to be the successor:

https://lucumr.pocoo.org/2024/2/15/rye-grows-with-uv/

The scripts should all work as before.