[t-kalinowski]

Summary

Reuse cached Python resolutions when UV_CACHE_DIR or UV_PYTHON_INSTALL_DIR is set. Previously, any nonempty UV_* variable disabled cache reuse, even though these two variables are stable path inputs.

Including their effective paths in the cache key preserves reuse for identical settings while resolving again when either uv storage location changes.

User-facing changes

• Python dependencies no longer resolve again on every run solely because UV_CACHE_DIR or UV_PYTHON_INSTALL_DIR is set.
• Changing either path uses a separate cached resolution, so an interpreter from another uv storage location is not reused.

Internal changes

• Treat the two uv path variables as cache-key inputs while continuing to make other nonempty UV_* variables and RETICULATE_UV bypass the cache.
• Resolve relative uv paths against the current working directory before hashing them.
• Add public ir run coverage for reuse and isolation across multiple uv path combinations.

Testing

• cargo fmt --all -- --check
• cargo clippy --all-targets -- -D warnings
• cargo nextest run --no-fail-fast -j 4 (205 passed)