Add pyo3 feature forwarding

[jam1garner]

This is to allow users to directly control the features of the pyo3 instance used by inline-python without adding it as a direct dependency (and thus risking the versions of pyo3 drifting out of date without pinning both libraries versions). This is especially useful as inline-python re-exports pyo3.

The format used is "pyo3-{featurename}", following the kebab case of pyo3's features.

[de-vri-es]

Hey, thanks for the PR! I can certainly see the point of this, but I'm a little worried that we'll forget to keep it in sync in the future.

@m-ou-se: What do you think?

[jam1garner]

If keeping all the features in sync is a worry I would, at minimum, recommend forwarding the macros feature—without it you lose a lot of the ability to integrate with pyo3 (exposing user types/functions to python)