perf(client): reuse snpb.SubscribeResponse in RPC handler

[ijsong]

What this PR does

This pull request optimizes
internal/storagenode/client.(*LogClient).Subscribe. It reuses
snpb.SubscribeResponse to reduce heap allocations. Note that it does not reuse
the byte slice in the snpb.SubscribeResponse. It only reuses the struct
snpb.SubscribeResponse itself.

[ijsong]

• perf(client): use transmitResultPool to reduce heap allocs #722
• perf(client): prealloc pkg/varlog.(*transmitter).transmitQueue #721
• perf(client): optimize with atomic.Int64 for lastSubscribeAt in pkg/varlog.(subscriber) #720
• perf(client): reuse snpb.SubscribeResponse in RPC handler #719 👈
• perf(benchmark): use grpc.SharedBufferPool for grpc.DialOption #718
• ci: bump go.uber.org/mock/mockgen from v0.3.0 to v0.4.0 #733 : 1 other dependent PR (#732 )
• main

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[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 49.67%. Comparing base (fbf0c17) to head (890508d).

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #719      +/-   ##
==========================================
- Coverage   49.73%   49.67%   -0.06%     
==========================================
  Files         235      235              
  Lines       20715    20717       +2     
==========================================
- Hits        10302    10291      -11     
- Misses       9774     9783       +9     
- Partials      639      643       +4     

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[ijsong]

Merge activity

• Mar 5, 4:41 AM EST: @ijsong started a stack merge that includes this pull request via Graphite.
• Mar 5, 4:42 AM EST: Graphite rebased this pull request as part of a merge.
• Mar 5, 4:50 AM EST: @ijsong merged this pull request with Graphite.