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]

lighthouse/tests/beacon_node.rs

@@ -1927,22 +1927,43 @@ fn hdiff_buffer_cache_size_flag() {
         .flag("hdiff-buffer-cache-size", Some("1"))
         .run_with_zero_port()
         .with_config(|config| {
-            assert_eq!(config.store.hdiff_buffer_cache_size.get(), 1);
+            assert_eq!(config.store.cold_hdiff_buffer_cache_size.get(), 1);
         });
 }
 #[test]
 fn hdiff_buffer_cache_size_default() {
-    use beacon_node::beacon_chain::store::config::DEFAULT_HDIFF_BUFFER_CACHE_SIZE;
+    use beacon_node::beacon_chain::store::config::DEFAULT_COLD_HDIFF_BUFFER_CACHE_SIZE;
     CommandLineTest::new()
         .run_with_zero_port()
         .with_config(|config| {
             assert_eq!(
-                config.store.hdiff_buffer_cache_size,
-                DEFAULT_HDIFF_BUFFER_CACHE_SIZE
+                config.store.cold_hdiff_buffer_cache_size,
+                DEFAULT_COLD_HDIFF_BUFFER_CACHE_SIZE
             );
         });
 }
 #[test]
+fn hot_hdiff_buffer_cache_size_default() {
+    use beacon_node::beacon_chain::store::config::DEFAULT_HOT_HDIFF_BUFFER_CACHE_SIZE;
+    CommandLineTest::new()
+        .run_with_zero_port()
+        .with_config(|config| {
+            assert_eq!(
+                config.store.hot_hdiff_buffer_cache_size,
+                DEFAULT_HOT_HDIFF_BUFFER_CACHE_SIZE
+            );
+        });
+}
+#[test]
+fn hot_hdiff_buffer_cache_size_flag() {
+    CommandLineTest::new()
+        .flag("hot-hdiff-buffer-cache-size", Some("3"))
+        .run_with_zero_port()
+        .with_config(|config| {
+            assert_eq!(config.store.hot_hdiff_buffer_cache_size.get(), 3);
+        });
+}
+#[test]
 fn auto_compact_db_flag() {
     CommandLineTest::new()
         .flag("auto-compact-db", Some("false"))