Add conversion support for either::Either

[aldanor]

Added conversion support for either's Either<L, R> type, equivalent to Union[L, R] on the Python side.

It's a tiny but pretty popular crate, with 24k dependent crates and 6-7M downloads/m.

It also simplifies a very common use case of accepting or returning one of the two types, without having to define a helper enum for each particular case.

[aldanor]

Btw the errors that appear on CI:

---- conversions::chrono::tests::test_pyo3_time_frompyobject stdout ----
thread 'conversions::chrono::tests::test_pyo3_time_frompyobject' panicked at 'called `Result::unwrap()` on an `Err` value: PyErr { type: <class 'ValueError'>, value: ValueError('invalid or out-of-range time'), traceback: None }', src/conversions/chrono.rs:833:60

I was also seeing locally (on M1), was assuming it's some local problem, but apparently not...

[adamreichold]

I was also seeing locally (on M1), was assuming it's some local problem, but apparently not...

You might be seeing fallout from #3424.

[davidhewitt]

Yes I'm working on a pr to fix the chrono problem, will try to push later

[codspeed-hq]

CodSpeed Performance Report

Merging #3456 will improve performances by 22.57%

_{Comparing aldanor:feature/either (a75464e) with main (31b871a)}

Summary

⚡ 1 improvements
✅ 77 untouched benchmarks

Benchmarks breakdown

	Benchmark	main	aldanor:feature/either	Change
⚡	list_via_extract	301.7 ns	246.1 ns	+22.57%