This PR fixes a bug with the current implementation for Model2Vec
embeddings where `embed_documents` does not work as expected.
- **Description**: the current implementation uses `encode_as_sequence`
for encoding documents. This is incorrect, as `encode_as_sequence`
creates token embeddings and not mean embeddings. The normal `encode`
function handles both single and batched inputs and should be used
instead. The return type was also incorrect, as encode returns a NumPy
array. This PR converts the embedding to a list so that the output is
consistent with the Embeddings ABC.