Migrate Poetry package metadata

[mkniewallner]

Right now, Poetry package specification defined in packages and include/exclude is not converted, with a warning displayed if those keys are found.

uv build backend is currently in preview (astral-sh/uv#8779), and could change before it is considered stable, so it's probably safe to not implement this right now, or to use a different build backend in the meantime (for instance hatchling, which is also the default backend used by uv when creating a library).

[mkniewallner]

One way to implement that could be to default to a stable build backend for the migration, and add a --build-backend argument to be able to choose uv (with maybe a warning to warn users that this is not stable yet).