Add sorting parameter to search_memories interface

[abrookins]

The VectorStoreAdapter.search_memories() interface doesn't accept a sorting parameter. This is tricky because we're trying to make vector stores pluggable with LangChain's vector store interfaces, which are limited -- most parameters other than similarity threshold are outside of the interface and vendor-specific.

Once the parameter exists in our interface, however we choose to implement it, we need to thread it through the places we call search_memories.