CrateDB does not understand `CREATE INDEX`

[amotl]

Problem

When a model includes a column definition like this,

idx = Column(Integer, index=True)

the CrateDB SQLAlchemy dialect trips.

E               sqlalchemy.exc.ProgrammingError: (crate.client.exceptions.ProgrammingError) SQLParseException[line 1:8: no viable alternative at input 'CREATE INDEX']
E               [SQL: CREATE INDEX ix_full_md5_llm_cache_llm ON full_md5_llm_cache (llm)]
E               (Background on this error at: https://sqlalche.me/e/20/f405)

../../../.venv/lib/python3.12/site-packages/crate/client/http.py:238: ProgrammingError

[amotl]

This PR includes an easy monkey patch.

• Cache: Add CrateDBCache and CrateDBSemanticCache langchain-cratedb#12

[amotl]

• That's a patch, broken out of another one: Compiler: Make CREATE INDEX a no-op #214.