feat: client side metrics

[daniel-sanche]

This PR adds the overall structure for collecting client-side metrics, and writing them to OpenTelemetry.

Reviewers: Look at the _metrics folder first for the atchitecture of how metrics are handled. Then look at the client, _read_rows, and _mutate_rows files to see how it is used in the library. If this PR is too large to review at once, let me know and I can break it up into chunks, now that I have the overall structure in place

Benhmarking:

• recording metrics without application_blocking or throttling seems to put this at a similar read_rows performance as before (~75k rps, +/- 5k)
• recording metrics with application_blocking tracking included seems to have added ~5% cost to read_rows (seeing runs between 69-73k rps)

TODO (future PRs):

• grpc channel throttling latencies
• system tests
• otel exporter

[daniel-sanche]

Also any idea how much overhead this adds?

I haven't had a chance to do benchmarks with this yet. The ones I'm most concerned about are the two I haven't added yet: application_blocking_latencies and throttling_latencies

[daniel-sanche]

closing in favor of smaller PRs