perf(grpc): switch to gRPC CodecV2 for improved performance

[ijsong]

What this PR does

This PR updates the gRPC codec from v1 to v2, enhancing performance and reducing
memory allocations by utilizing a memory pool for encoded messages.

Refs:

• Implement new Codec that uses mem.BufferSlice instead of []byte grpc/grpc-go#7356
• grpc: upgrade to 1.66.2 and use Codec v2 vitessio/vitess#16790

[codecov]

Codecov Report

Attention: Patch coverage is 73.07692% with 7 lines in your changes missing coverage. Please review.

Project coverage is 78.77%. Comparing base (433a510) to head (da60029).

Files with missing lines	Patch %	Lines
pkg/rpc/codec.go	73.07%	5 Missing and 2 partials ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #944      +/-   ##
==========================================
- Coverage   78.95%   78.77%   -0.19%     
==========================================
  Files         180      180              
  Lines       21621    21636      +15     
==========================================
- Hits        17071    17043      -28     
- Misses       3730     3758      +28     
- Partials      820      835      +15     

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