pagserver: use vectored read path in benchmarks

[VladLazar]

Problem

Benchmarks don't use the vectored read path.

Summary of changes

• Update the benchmarks to use the vectored read path for both singular and vectored gets.
• Disable validation for the benchmarks

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]

2876 tests run: 2742 passed, 0 failed, 134 skipped (full report)

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Flaky tests (1)

Postgres 15

• test_partial_evict_tenant[relative_spare]: release

Code coverage* (full report)

• functions: 28.3% (6546 of 23138 functions)
• lines: 47.0% (46220 of 98421 lines)

* collected from Rust tests only

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_{The comment gets automatically updated with the latest test results
8e26c16 at 2024-04-29T09:46:45.238Z :recycle:}