moving LastWrittenLSNCache to Neon Extension

[thesuhas]

Problem

We currently have this code duplicated across different PG versions. Moving this to an extension would reduce duplication and simplify maintenance.

Summary of changes

Moving the LastWrittenLSN code from PG versions to the Neon extension and linking it with hooks.

Related Postgres PR: neondatabase/postgres#590

Closes: #10973

[github-actions]

If this PR added a GUC in the Postgres fork or neon extension,
please regenerate the Postgres settings in the cloud repo:

make NEON_WORKDIR=path/to/neon/checkout \
  -C goapp/internal/shareddomain/postgres generate

If you're an external contributor, a Neon employee will assist in
making sure this step is done.

[github-actions]

7909 tests run: 7524 passed, 0 failed, 385 skipped (full report)

---

Code coverage* (full report)

• functions: 32.5% (8730 of 26869 functions)
• lines: 48.5% (74669 of 153983 lines)

* collected from Rust tests only

---

_{The comment gets automatically updated with the latest test results
6df3fc1 at 2025-03-12T19:09:05.383Z :recycle:}

[MMeent]

The PG17 tests timeout after many failures.

Personal experience would point to something that causes segfaults/panics/Assertion failures thus causing core dumps, which somehow makes the whole system slow to a halt.

[thesuhas]

The PG17 tests timeout after many failures.

Personal experience would point to something that causes segfaults/panics/Assertion failures thus causing core dumps, which somehow makes the whole system slow to a halt.

Could there be a reason why this only happens in one of the PG17 test suites? Is there something different/unique about that test?

[MMeent]

Could there be a reason why this only happens in one of the PG17 test suites? Is there something different/unique about that test?

It looks like it is the only test running debug+without_lfc, so that's probably a good indication?