fix icechunk dims

[lazarusA]

fixes #628 #627

[gemini-code-assist]

Code Review

This pull request refactors the Zarr loading logic by centralizing operations in ZarrLoaderLRU.ts and delegating store-specific tasks to icechunk-store.ts and zarrita-store.ts. It also introduces a comprehensive set of shared utilities in utils.ts for path handling, size summaries, and retry mechanisms. The review feedback identifies several high-priority improvements: parallelizing dimension fetching to improve performance, adding safety checks for JSON parsing of metadata, fixing dimension resolution for variables within sub-groups, and correcting the fallback logic for missing dimension arrays in the cache to respect the actual dimension shape.