Hierarchical state diffs in hot DB (#6750)

This PR implements https://github.com/sigp/lighthouse/pull/5978 (tree-states) but on the hot DB. It allows Lighthouse to massively reduce its disk footprint during non-finality and overall I/O in all cases.

Closes https://github.com/sigp/lighthouse/issues/6580

Conga into https://github.com/sigp/lighthouse/pull/6744

### TODOs

- [x] Fix OOM in CI https://github.com/sigp/lighthouse/pull/7176
- [x] optimise store_hot_state to avoid storing a duplicate state if the summary already exists (should be safe from races now that pruning is cleaner)
- [x] mispelled: get_ancenstor_state_root
- [x] get_ancestor_state_root should use state summaries
- [x] Prevent split from changing during ancestor calc
- [x] Use same hierarchy for hot and cold

### TODO Good optimization for future PRs

- [ ] On the migration, if the latest hot snapshot is aligned with the cold snapshot migrate the diffs instead of the full states.
```
align slot  time
10485760    Nov-26-2024
12582912    Sep-14-2025
14680064    Jul-02-2026
```

### TODO Maybe things good to have

- [ ] Rename anchor_slot https://github.com/sigp/lighthouse/compare/tree-states-hot-rebase-oom...dapplion:lighthouse:tree-states-hot-anchor-slot-rename?expand=1
- [ ] Make anchor fields not public such that they must be mutated through a method. To prevent un-wanted changes of the anchor_slot

### NOTTODO

- [ ] Use fork-choice and a new method [`descendants_of_checkpoint`](ca2388e196 (diff-046fbdb517ca16b80e4464c2c824cf001a74a0a94ac0065e635768ac391062a8)) to filter only the state summaries that descend of finalized checkpoint]

book/src/help_bn.md

@@ -171,10 +171,10 @@ Options:
           Specify your custom graffiti to be included in blocks. Defaults to the
           current version and commit, truncated to fit in 32 bytes.
       --hdiff-buffer-cache-size <SIZE>
-          Number of hierarchical diff (hdiff) buffers to cache in memory. Each
-          buffer is around the size of a BeaconState so you should be cautious
-          about setting this value too high. This flag is irrelevant for most
-          nodes, which run with state pruning enabled. [default: 16]
+          Number of cold hierarchical diff (hdiff) buffers to cache in memory.
+          Each buffer is around the size of a BeaconState so you should be
+          cautious about setting this value too high. This flag is irrelevant
+          for most nodes, which run with state pruning enabled. [default: 16]
       --hierarchy-exponents <EXPONENTS>
           Specifies the frequency for storing full state snapshots and
           hierarchical diffs in the freezer DB. Accepts a comma-separated list
@@ -187,6 +187,12 @@ Options:
       --historic-state-cache-size <SIZE>
           Specifies how many states from the freezer database should be cached
           in memory [default: 1]
+      --hot-hdiff-buffer-cache-size <SIZE>
+          Number of hot hierarchical diff (hdiff) buffers to cache in memory.
+          Each buffer is around the size of a BeaconState so you should be
+          cautious about setting this value too high. Setting this value higher
+          can reduce the time taken to store new states on disk at the cost of
+          higher memory usage. [default: 1]
       --http-address <ADDRESS>
           Set the listen address for the RESTful HTTP API server.
       --http-allow-origin <ORIGIN>