Add find_all_with to batch Group members lookup and eliminate N+1 in PATCH

[shuyahonda]

Addresses issue #157: Resolve N+1 queries on Group PATCH when resolving members (users)

Approach

• Batch member resolution via find_all_with: Add a batch-lookup hook to dynamic list mappings that is preferred over per-item find_with. This allows fetching all referenced users in one query for Group PATCH.
• Backward compatible: If find_all_with is not provided, existing find_with continues to be used.
• Minimal mock for tests: Introduce a dedicated MockBatchGroupsController/Model that uses find_all_with (users-only) to verify the end-to-end behavior without overcomplicating the mock.

Changes

• Batch support: Prefer :find_all_with over :find_with in dynamic list mappings during from_scim!/from_scim_patch!.
• Documentation/comments: Updated inline comments to explain find_all_with and precedence.

[pond]

Awesome patch! Thanks so much 😀

[alexmingoia]

Thank you so much for this. Just saved me a late night on-call 👍