feat: Prune uv workspaces (#13613)
### Description
Add uv-aware pruning for pure Python and mixed JavaScript/Python
repositories. Pruning keeps the reachable workspace and external
dependency closure, rewrites root workspace members and
`[tool.uv.sources]`, preserves lockfile fidelity, and carries required
uv/Python configuration into the output without invoking `uv`.
### Testing Instructions
- Run `cargo test -p turborepo-lockfiles uv`.
- Run `cargo test -p turborepo-repository uv`.
- When `uv` is installed, verify pruned output with `uv lock --check`.
<sub>Closes TURBO-5854</sub>
