Feature request: Allow each python package to have its own julia environment?

Different python packages may have conflicting requirements. It seems like the more flexible approach would be to allow to different python packages to specify that they need their own julia environment (rather than one for all python packages in a conda env), or even that this would be default.

The issue does not name files, tests, or entry points. Start by tracing how pyjuliapkg currently chooses and shares Julia environments across Python packages, then identify how package-specific configuration could be represented. Done means defining and implementing a clear behavior for independent environments, including the default and conflicting dependency cases.

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