Implement pycapsule for schema

[timsaucer]

This PR adds support for converting internal rerun schema to pyarrow schema.

If you have a schema object you can do

now_schema = pa.schema(old_schema)

[github-actions]

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Result	Commit	Link	Manifest
✅	e63d9b4	https://rerun.io/viewer/pr/12199	+nightly +main

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[swallez]

Nice!