chore(pageserver): separate missing key error

[skyzh]

Problem

As part of #7375 and to improve the current vectored get implementation, we separate the missing key error out. This also saves us several Box allocations in the get page implementation.

Summary of changes

• Create a caching field of layer traversal id for each of the layer.
• Remove box allocations for layer traversal id retrieval and implement MissingKey error message as before. This should be a little bit faster.
• Do not format error message until Display.
• For in-mem layer, the descriptor is different before/after frozen. I'm using once lock for that.

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

[VladLazar]

Nice change. Some comments inline.

[github-actions]

2772 tests run: 2654 passed, 0 failed, 118 skipped (full report)

---

Code coverage* (full report)

• functions: 28.1% (6464 of 23041 functions)
• lines: 46.8% (45671 of 97588 lines)

* collected from Rust tests only

---

_{The comment gets automatically updated with the latest test results
57e33fd at 2024-04-22T14:45:45.858Z :recycle:}