Fix CompressedLeafNode type compatibility and enhance trait implementations

- Fix capacity/len fields from u16 to usize for LeafNode compatibility
- Adjust data array size from 248 to 236 bytes to maintain 256-byte total
- Add missing LeafNode compatibility methods: keys(), values(), values_mut()
- Implement PartialEq and Eq traits for node comparison
- Add From<LeafNode> trait for seamless conversion between node types
- Update all method signatures and calculations for usize types
- Add comprehensive tests for new trait implementations
- Remove obsolete new_with_usize_capacity method and related tests
- Ensure full API compatibility between CompressedLeafNode and LeafNode

Co-authored-by: Ona <no-reply@ona.com>

Author: KentBeck