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]

beacon_node/store/src/historic_state_cache.rs

@@ -34,11 +34,17 @@ impl<E: EthSpec> HistoricStateCache<E> {
 
     pub fn get_hdiff_buffer(&mut self, slot: Slot) -> Option<HDiffBuffer> {
         if let Some(buffer_ref) = self.hdiff_buffers.get(&slot) {
-            let _timer = metrics::start_timer(&metrics::BEACON_HDIFF_BUFFER_CLONE_TIMES);
+            let _timer = metrics::start_timer_vec(
+                &metrics::BEACON_HDIFF_BUFFER_CLONE_TIME,
+                metrics::COLD_METRIC,
+            );
             Some(buffer_ref.clone())
         } else if let Some(state) = self.states.get(&slot) {
             let buffer = HDiffBuffer::from_state(state.clone());
-            let _timer = metrics::start_timer(&metrics::BEACON_HDIFF_BUFFER_CLONE_TIMES);
+            let _timer = metrics::start_timer_vec(
+                &metrics::BEACON_HDIFF_BUFFER_CLONE_TIME,
+                metrics::COLD_METRIC,
+            );
             let cloned = buffer.clone();
             drop(_timer);
             self.hdiff_buffers.put(slot, cloned);