Add support for from_py_with on struct tuples and enums

[ricohageman]

Fixes #1441 by introducing from_py_with for tuple structs and enum.

[adamreichold]

Concerning the failing test, isnt't the

obj.get_refcnt(unsafe { Python::assume_gil_acquired() })

part directly after releasing the GIL indeed not well-defined as it races with other test threads acquiring the GIL?

[adamreichold]

Concerning the failing test

This is obviously unrelated to this PR, I just wanted to bring it up so people more acquainted with that part of the code can shed some light on this.

[mejrs]

Concerning the failing test, isnt't the

obj.get_refcnt(unsafe { Python::assume_gil_acquired() })

part directly after releasing the GIL indeed not well-defined as it races with other test threads acquiring the GIL?

Yes, this test should probably be rewritten. I'll do that in a bit.

[davidhewitt]

Thank you, very grateful to see this implemented! It could be worth checking the guide to see if any documentation there would benefit from updating.

[ricohageman]

@davidhewitt thanks for pointing out the documentation. Currently the from_py_with annotation is only documented for functions. I would have expected it to be there for struct when it was introduced for normal structs. I've added some information regarding this feature.