removes `NotA`

[JojiiOfficial]

Removes the NotA error type and replaces it with the new QdrantError. This is a breaking change for clients that expect the error type to be anyhow::Result. Feel free to close the PR if we don't actually want breaking changes anymore since we won't introduce ones with the new Qdrant client

[timvisee]

This is a breaking change for clients that expect the error type to be anyhow::Result.

I'm afraid we cannot do it right away then.

Would it be possible to keep it for the existing client, but use the type error in the new client? Maybe we can eventually totally remove it once we deprecate/remove the old client.