feat(pageserver): gc-compaction split job and partial scheduler (#9897)

## Problem

part of https://github.com/neondatabase/neon/issues/9114, stacked PR
over #9809

The compaction scheduler now schedules partial compaction jobs.

## Summary of changes

* Add the compaction job splitter based on size.
* Schedule subcompactions using the compaction scheduler.
* Test subcompaction scheduler in the smoke regress test.
* Temporarily disable layer map checks

---------

Signed-off-by: Alex Chi Z <chi@neon.tech>

test_runner/regress/test_compaction.py

@@ -159,6 +159,7 @@ def test_pageserver_gc_compaction_smoke(neon_env_builder: NeonEnvBuilder):
             enhanced_gc_bottom_most_compaction=True,
             body={
                 "scheduled": True,
+                "sub_compaction": True,
                 "compact_range": {
                     "start": "000000000000000000000000000000000000",
                     # skip the SLRU range for now -- it races with get-lsn-by-timestamp, TODO: fix this