Rewrite Python interpreter discovery

[zanieb]

Updates our Python interpreter discovery to conform to the rules described in #2386, please see that issue for a full description of the behavior. Briefly, we now will search for interpreters that satisfy a requested version without stopping at the first Python executable. We also add the plumbing necessary to request Python implementations other than CPython, though we do not add support for other implementations at this time.

A major internal goal of this work is to prepare for user-facing managed toolchains i.e. fetching a requested version during uv run. These APIs are not introduced, but there is some managed toolchain handling as required for our test suite.

Some noteworthy implementation changes:

• The uv_interpreter::find_python module has been removed in favor of a uv_interpreter::discovery module.
• There are new types to help structure interpreter requests and track sources
• Executable discovery is implemented as a big lazy iterator and is a central authority for source precedence
• uv_interpreter::Error variants were split into scoped types in each module

Remaining work:

• [ ] Write and merge new test cases to main
• [x] Fix Windows test cases
• [ ] Explore behavior around implementation precedence (i.e. CPython over PyPy)
• Future: Combine PythonVersion and VersionRequest
• Future: Consider splitting ManagedToolchain into local and remote variants

Refactors split into:

• 3329

• 3330

• 3331

• 3332

Closes #2386

[codspeed-hq[bot]]

CodSpeed Performance Report

Merging #3266 will not alter performance

_{Comparing zb/interp-request-ii (5152302) with main (18d229e)}

Summary

✅ 12 untouched benchmarks