Normalize Conda environment metadata cache keys

[karthiknadig]

Problem

PR #487 added a shared Conda environment metadata cache, but its keys use raw paths. On Windows, equivalent paths with different casing or separator forms can miss the cache and reduce cross-refresh reuse.

Copilot identified this during review after the original PR had already merged.

Acceptance criteria

• Normalize Conda environment metadata cache keys for lookup, insertion, removal, and pruning.
• Preserve fingerprint invalidation behavior.
• Keep targeted Conda tests and Rust pre-commit checks clean.

[karthiknadig]

Duplicate of #488, which was filed first and tracks the same raw-path cache-key issue. PR #490 is being retargeted to close #488.