net/http2: pool transport gzip readers

[AlexanderYastrebov]

This is a copy of the CL 510255 with the difference that
it preserves use of fs.ErrClosed when reading after close.

goos: darwin
goarch: arm64
pkg: golang.org/x/net/http2
cpu: Apple M4
│ HEAD~1 │ HEAD │
│ sec/op │ sec/op vs base │
ClientGzip-10 752.8µ ± 1% 750.7µ ± 2% ~ (p=0.393 n=10)

          │    HEAD~1    │                 HEAD                 │
          │     B/op     │     B/op      vs base                │

ClientGzip-10 75.49Ki ± 0% 33.98Ki ± 3% -54.99% (p=0.000 n=10)

          │   HEAD~1   │               HEAD                │
          │ allocs/op  │ allocs/op   vs base               │

ClientGzip-10 705.0 ± 0% 698.5 ± 0% -0.92% (p=0.000 n=10)

Updates golang/go#61353

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[gopherbot]

Message from Gopher Robot:

Patch Set 1:

(1 comment)

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Message from Alexander Yastrebov:

Patch Set 1:

(1 comment)

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Message from Sean Liao:

Patch Set 2: Commit-Queue+1

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Message from Go LUCI:

Patch Set 2:

Dry run: CV is trying the patch.

Bot data: {"action":"start","triggered_at":"2025-10-08T20:32:55Z","revision":"8e3e4d8fcffc1ff884c8c9290d9b1865375baa7b"}

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Patch Set 2: -Commit-Queue

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Patch Set 2:

This CL has passed the run

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Patch Set 2: LUCI-TryBot-Result+1

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Patch Set 2:

(1 comment)

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This PR (HEAD: 4d04dc9) has been imported to Gerrit for code review.

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Message from Alexander Yastrebov:

Patch Set 2:

(1 comment)

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