Speed up grpc fetch and query response parsing

[yorickvP]

Problem

Running a profiler on my pinecone-using application. it was CPU-bottlenecked on json_format.MessageToDict (being able to do about 100 vectors per second in query and fetch responses).
It turns out converting the embeddings to a dict this way is very slow. It's much faster to convert them to a list without going through MessageToDict.

Solution

Changed parse_fetch_response and parse_query_response to directly read the protobuf structure instead of going through MessageToDict

Type of Change

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)
• This change requires a documentation update
• Infrastructure change (CI configs, etc)
• Non-code change (docs, etc)
• None of the above: (explain here)

Test Plan

Describe specific steps for validating this change.

• Ran make test-grpc-unit.