Add support for multiple input files

`uv` supports passing any number of requirements.in files, and also any number of pyproject.toml files. This can be useful if your dependencies are split across multiple tools that are consumed in other ways, so you don't want to duplicate their requirements. I haven't tried but it looks like I could potentially hack this with `data` + `args`, but I think it would be nice if this was supported.

Start by reading uv's handling of requirements.in and pyproject.toml inputs, then inspect the repository's current rule entry point and tests for single-file inputs. Done means the rule accepts any number of each supported input file and consumes dependencies from all of them as intended.

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