grpc: upgrade to 1.66.2 and use Codec v2

[vmg]

Description

This PR upgrades our GRPC version to 1.66.2 and introduces the new Codec v2 for serializing and deserializing protobuf messages. The goal of this codec is to enable memory pooling and hopefully increase real-world performance of Vitess clusters by reducing the number of memory allocations used when working with GRPC. You can can read up on the implementation details and next steps for the codec in this discussion PR.

This is the very first iteration of these changes, which only implements buffer pooling, but does not attempt to pool the objects themselves. Our hope is that this should already show in the benchmarks, so if it doesn't it'll be a bit disappointing! 🤞

Related Issue(s)

• codec: implement codec v2 planetscale/vtprotobuf#138

Checklist

• "Backport to:" labels have been added if this change should be back-ported to release branches
• If this change is to be back-ported to previous releases, a justification is included in the PR description
• Tests were added or are not required
• Did the new or modified tests pass consistently locally and on CI?
• Documentation was added or is not required

Deployment Notes

[vitess-bot]

Review Checklist

Hello reviewers! 👋 Please follow this checklist when reviewing this Pull Request.

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[vitess-bot]

Hello! 👋

This Pull Request is now handled by arewefastyet. The current HEAD and future commits will be benchmarked.

You can find the performance comparison on the arewefastyet website.