net/http/internal/http2: optimize Date header generation

[solos]

Replace the per-request time.Now().UTC().Format() call
in writeChunk with a cached string that updates at most
once per UTC second.

This eliminates redundant time formatting overhead in
high-concurrency HTTP/2 workloads by using an atomic
cache for the formatted date string.

Fixes #79914

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Patch Set 1:

(1 comment)

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