Add Usage to QueryResponseWithUnsignedIndices

[austin-denoble]

Problem

Usage is now returned for data plane operations against serverless indexes. This was included in the codebase in this PR where we replaced the vector_service.proto file with generated classes that included the most recent changes to the data plane including read units: #66

However, the newer QueryResponseWithUnsignedIndices class does not map usage so it gets dropped for query requests using this class.

Solution

Update QueryResponseWithUnsignedIndices to handle usage.
I also added toString() overrides to all of the classes in unsigned_indices_model since debugging/logging was difficult without it.

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

Integration tests for this are pending, I believe @rohanshah18 has integration test changes in flight so I didn't make any changes there. We should add assertions on queryResponse.getUsage().getReadUnits().

I've run data plane operations locally using the examples folder to validate that we're seeing usage and read units on data plane responses.

[rohanshah18]

Thanks for making this change, LGTM.