Embedding function should always return a list of a list of vectors

[paubins2]

Why are these changes needed?

The PGVectorDB conforms to VectorDB, however it ignores the method signature for the embedding function.

Optional[Callable[[List[str]], List[List[float]]]]

Changing the embedding function to always expect a list of lists rather than a tensor.

Related issue number

Checks

• I've included any doc changes needed for https://microsoft.github.io/autogen/. See https://microsoft.github.io/autogen/docs/Contribute#documentation to build and test documentation locally.
• I've added tests (if relevant) corresponding to the changes introduced in this PR.
• I've made sure all auto checks have passed.

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GitGuardian id	GitGuardian status	Secret	Commit	Filename
12853598	Triggered	Generic High Entropy Secret	535eeae	test/oai/test_utils.py	View secret
10404693	Triggered	Generic High Entropy Secret	535eeae	test/oai/test_utils.py	View secret
12853599	Triggered	Generic High Entropy Secret	535eeae	test/oai/test_utils.py	View secret
10404694	Triggered	Generic High Entropy Secret	535eeae	test/oai/test_utils.py	View secret
12853601	Triggered	Generic High Entropy Secret	535eeae	test/oai/test_utils.py	View secret
10404696	Triggered	Generic High Entropy Secret	535eeae	test/oai/test_utils.py	View secret
10422482	Triggered	Generic High Entropy Secret	535eeae	test/oai/test_utils.py	View secret
12853602	Triggered	Generic High Entropy Secret	535eeae	test/oai/test_utils.py	View secret

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[thinkall]

Thank you @paubins2 for the PR! mongodb.py has the same issue, would you like to fix that as well?