Optimize `HybridRouter` dependencies

[jamescalam]

I want us to work on dependencies for hybrid usage of SR, there are a few issues / things to optimize:

• Fully drop pinecone-text library use, we should swap to our own local bm25 calculation or using alternative, more active, library that supports bm25 vectors.
• Allow users to use HybridRouter without needing to install local hybrid dependencies. Right now a user must install semantic-router[hybrid] to use the HybridRouter. We should drop that requirement in favour allowing various dependencies to support hybrid (such as AurelioBM25Encoder or BM25Encoder, not both). I'd like to get support for sentence-transformer sparse encoders asap too, so just factor that future thing into development on this task.