pageserver: implement aligned io buffer

[yliang412]

Problem

Summary of changes

Checklist before requesting a review

• I have performed a self-review of my code.
• If it is a core feature, I have added thorough tests.
• Do we need to implement analytics? if so did you add the relevant metrics to the dashboard?
• If this PR requires public announcement, mark it with /release-notes label and add several sentences in this section.

Checklist before merging

• Do not forget to reformat commit message to not include the above checklist

[github-actions]

5085 tests run: 4878 passed, 0 failed, 207 skipped (full report)

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Flaky tests (4)

Postgres 17

• test_cli_start_stop_multi: debug-x86-64

Postgres 16

• test_multixid_wraparound_import: release-x86-64

Postgres 15

• test_readonly_node_gc: release-arm64

Postgres 14

• test_timeline_delete_works_for_remote_smoke: release-arm64

Code coverage* (full report)

• functions: 31.6% (7578 of 23995 functions)
• lines: 49.7% (60572 of 121930 lines)

* collected from Rust tests only

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_{The comment gets automatically updated with the latest test results
3ee9877 at 2024-10-07T20:47:48.274Z :recycle:}

[yliang412]

Implemented in #9326