Custom schema support (#254)

implements custom schema based on
https://github.com/langchain-ai/langchain-weaviate/pull/201

- Added tests both for this feature and for using `simsimd` and
increasing test coverage (see
https://github.com/langchain-ai/langchain-weaviate/pull/249)
- `use_multi_tenancy` can be both Bool and Dict, for fine grained config
of MT Collections. (Ignored if schema is provided)
- You can now pass a `schema` parameter when creating a new collection.
[Check here for a an easy way to create your schema
json/dict](https://dudanogueira.github.io/weaviate-add-collection/).
- Multi Tenancy: auto ON for autoTenantCreation and autoTenantActivation
- Add some more tests for vector store and _math.py
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Co-authored-by: dhanshew72 <d.hanshew@aol.com>