release-8.1: Fix prefetch buffer and GCS EOF retry (#59496, #59851)

[GMHDBJD]

This PR manually cherry-picks two PRs to release-8.1 to resolve a dependency.

---

cherry-pick #59496
cherry-pick #59851

What problem does this PR solve?

Issue Number: close #59495, close #59754

Problem Summary:
This PR addresses two separate but related issues:

1. The prefetch buffer was not always being fully filled, potentially leading to inefficient reads.
2. A bug in Go's net/http library can cause io.EOF errors when using GCS, which were not being retried, causing operations to fail.

What changed and how does it work?

1. Prefetch Buffer Fix: Switched to using io.ReadFull to ensure the prefetch buffer is always filled completely.
2. GCS EOF Retry: Added a workaround in the GCS storage layer to specifically retry on io.EOF errors, making the connection more resilient to the underlying library bug.

Check List

Tests

• Unit test
• Integration test
• Manual test (add detailed scripts or steps below)
• No need to test

Release note

None

[tiprow]

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[Benjamin2037]

LGTM

[ti-chi-bot]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: Benjamin2037, D3Hunter

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[ti-chi-bot]

[LGTM Timeline notifier]

Timeline:

• 2025-07-01 01:11:50.773519637 +0000 UTC m=+1357363.496698618: ☑️ agreed by Benjamin2037.
• 2025-07-01 02:15:47.465955107 +0000 UTC m=+1361200.189134086: ☑️ agreed by D3Hunter.

[GMHDBJD]

/retest

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[GMHDBJD]

/retest

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[codecov]

Codecov Report

Attention: Patch coverage is 53.84615% with 6 lines in your changes missing coverage. Please review.

Please upload report for BASE (release-8.1@61d7f3c). Learn more about missing BASE report.

Additional details and impacted files

@@               Coverage Diff                @@
##             release-8.1     #62060   +/-   ##
================================================
  Coverage               ?   71.2240%           
================================================
  Files                  ?       1469           
  Lines                  ?     424455           
  Branches               ?          0           
================================================
  Hits                   ?     302314           
  Misses                 ?     101587           
  Partials               ?      20554           

Flag	Coverage Δ
unit	71.2240% <53.8461%> (?)

Flags with carried forward coverage won't be shown. Click here to find out more.

Components	Coverage Δ
dumpling	52.9656% <0.0000%> (?)
parser	∅ <0.0000%> (?)
br	41.4333% <0.0000%> (?)

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[D3Hunter]

/retest

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