docs(storage): add zonal bucket pre-warmed writer pool sample

[NickGoog]

Adds optimizeWriteLatencyPool sample (region tag: storage_optimize_write_latency_pool) demonstrating a pre-warmed pool of zonal bucket writers with FinalizeOnClose = false and Flush() to avoid object creation and finalization metadata overhead on the critical write path.

Verified with both mock unit tests and live integration testing against a Rapid (zonal) bucket in us-central1-a:

Running live Go test against bucket=, prefix=live_go_pool_1790087532323
Go 1. Init pool (3 writers): 1.075960737s
Go 2. Write+flush: 26.459652ms
Go 4. Read back: "0123456789", pool size after refill: 3
--- PASS: TestWriterPoolGoSample (1.40s)
PASS

Description

Fixes #

Ask me for bug ID

Checklist

• I have followed Contributing Guidelines from CONTRIBUTING.MD
• Tests pass: go test -v ./... (see Testing)
• Code formatted: gofmt (see Formatting)
• Vetting pass: go vet (see Formatting)
• These samples need a new API enabled in testing projects to pass (N/A - uses existing Cloud Storage API)
• These samples need a new/updated env vars in testing projects set to pass (N/A - uses existing testing env vars)
• This sample adds a new sample directory, and I updated the CODEOWNERS file with the codeowners for this sample (N/A - added to existing storage/rapid directory)
• This sample adds a new Product API, and I updated the Blunderbuss issue/PR auto-assigner with the codeowners for this sample (N/A - Cloud Storage is an existing product)
• Please merge this PR for me once it is approved

[snippet-bot]

Here is the summary of changes.

You are about to add 1 region tag.

• storage/bidi/optimize_write_latency_pool.go:17, tag storage_optimize_write_latency_pool

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[gemini-code-assist]

Code Review

This pull request introduces optimizeWriteLatencyPool in storage/rapid/optimize_write_latency_pool.go to optimize write latency using a pre-warmed pool of writers for zonal buckets, along with corresponding unit tests in storage/rapid/rapid_test.go. The review feedback recommends handling and logging errors in the background goroutine when pre-warming a replacement writer fails, rather than silently ignoring them, to prevent debugging difficulties.

[tritone]

@cpriti-os would you mind reviewing/approving this one?