Unify editable and unnamed URL parsing

[charliermarsh]

Summary

This will help prevent bugs like #3934 by unifying the implementations for editables and non-editable unnamed requirements. Specifically, both of these now go through the same parsing paths and use the same struct representations (with the exception that the editable flag is flipped in the first case):

-e ./foo/bar
./foo/bar

We also now support PEP 508 in editable URLs. It turns out this is just a limitation in pip, so it's correct to support it. For example, this now works:

-e black[d] @ file://${PROJECT_ROOT}/scripts/packages/black_editable

Closes #3941.

Closes #3942.

[codspeed-hq]

CodSpeed Performance Report

Merging #3946 will improve performances by 6.5%

_{Comparing charlie/editable-url (8146a88) with main (8c11f99)}

Summary

⚡ 1 improvements
✅ 12 untouched benchmarks

Benchmarks breakdown

	Benchmark	main	charlie/editable-url	Change
⚡	wheelname_tag_compatibility[flyte-short-incompatible]	955.8 ns	897.5 ns	+6.5%

[charliermarsh]

Deleted a few hundred lines of code but added a few hundred in tests and snapshots.