Python: ideas for multiple modules

[kylebarron]

• Move Rust modules into workspace. Make crates/ top level directory?
• All crates/dirs inside crates/ are published to crates.io
• Make geoarrow-python crate inside crates/ with the rlib bindings to pyo3
• Convert existing geoarrow.rust.core code to only import from geoarrow-python and create a #[pymodule]
• Make a top-level function in geoarrow.rust.core named from_arrow which takes in any Arrow object (via pycapsule) and returns either a geometry array, chunked array, or table.
• Make tiny structs inside geoarrow-python that are just ArrowArray, ArrowSchema and ArrowStream to hold arbitrary pycapsule objects.
• Then a new geoarrow.rust.proj module can have functions that operate on any geoarrow input via pycapsule and return the above Arrow* minimal classes.

Ref #454