Refactor tests (#149)

This pull request updates the fake embeddings used for testing purposes.
It includes the following changes:

- Use consistent fake embeddings instead of openai embeddings.

- Moved all tests to the unit test folder.

- Raised the minimum test coverage to 96.44%

---------

Signed-off-by: hsm207 <hsm207@users.noreply.github.com>

Author: hsm207

.github/workflows/prebuild.yml

@@ -44,6 +44,4 @@ jobs:
           poetry run pytest -n `nproc` \
             --cov=langchain_weaviate \
             --cov-report term-missing \
-            --cov-fail-under=94.59
-        env:
-          OPENAI_API_KEY=${{ secrets.OPENAI_API_KEY_FROM_WEAVIATE }}
+            --cov-fail-under=96.44