fix: preserve relative paths in lockfile

[baszalmstra]

Description

pep508_rs::VerbatimUrl's Display and Serialize impls both write the parsed (normalized) URL and ignore the given string. So any pep508_rs::Requirement that goes through a string round-trip loses its verbatim spelling. The plural convert_uv_requirements_to_pep508 did exactly that:

let requirement = r.to_string();
pep508_rs::Requirement::from_str(&requirement)

For a tool.uv.sources path entry like my-subdir = { path = "my_subdir" }, this produced a Requirement whose VerbatimUrl::given() was the absolute file:// URL of the resolved path. rattler_lock's serializer (requirement_to_string) prefers given(), so the absolute path ended up baked into pixi.lock, breaking sharing across machines.

The sibling to_requirements (singular, for uv_distribution_types::Requirement) already handled this by carrying verbatim.given() over onto a fresh pep508_rs::VerbatimUrl::with_given(...). This PR applies the same treatment to the plural function.

Before:

requires_dist:
  - my-subdir @ file:///tmp/repro/my_subdir

After:

requires_dist:
  - my-subdir @ my_subdir

Fixes #4680

How Has This Been Tested?

• New unit test relative_path_requirement_round_trip_keeps_given in pixi_uv_conversions::conversions builds a uv Requirement<VerbatimParsedUrl> for my-subdir @ ./my_subdir, runs it through convert_uv_requirements_to_pep508, and asserts the resulting VerbatimUrl::given() is Some("./my_subdir"). The test fails on main and passes after the fix.
• Full pixi_uv_conversions lib (14 tests) and pixi_core lib (225 tests) suites pass.
• End-to-end against gabrieldemarmiesse/pixi-bug-repro: deleted the committed pixi.lock, ran the patched binary, and confirmed the regenerated lockfile contains my-subdir @ my_subdir rather than the absolute file:///... URL.

AI Disclosure

• This PR contains AI-generated content.
  • I have tested any AI-generated content in my PR.
  • I take responsibility for any AI-generated content in my PR.

Tools: Claude Code (Opus 4.7)

Checklist:

• I have performed a self-review of my own code
• I have commented my code, particularly in hard-to-understand areas
• I have added sufficient tests to cover my changes.

[hunger]

I think that will work.