Refactor: Add workspace cache to CoreUtilsMixin

[pyob-bot]

Summary of Changes

• Added _workspace_cache attribute to the CoreUtilsMixin class in src/pyob/core_utils.py.
• The cache is defined as a dictionary mapping strings to tuples of floats and strings, intended to store workspace-related metadata.

Technical Impact

• This change introduces a stateful caching mechanism to the mixin, allowing for future implementation of memoization or performance optimizations within workspace operations.
• No functional logic changes were introduced; this is a structural update to the class schema.