Moves lancedb from core dependencies to optional [memory] extras group
in pyproject.toml. This unblocks installation on Intel Macs where
lancedb>=0.29.2 has no macOS x86_64 wheels.
- Add try/except around lancedb import in lancedb_storage.py
- Raise clear ImportError with install instructions when lancedb is absent
- Add 6 tests covering optional dependency behavior
- Existing memory tests continue to pass
Closes#5327
Co-Authored-By: João <joao@crewai.com>
