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/iter.rs

@@ -384,9 +384,9 @@ fn slot_of_prev_restore_point<E: EthSpec>(current_slot: Slot) -> Slot {
 #[cfg(test)]
 mod test {
     use super::*;
-    use crate::StoreConfig as Config;
+    use crate::{MemoryStore, StoreConfig as Config};
     use beacon_chain::test_utils::BeaconChainHarness;
-    use beacon_chain::types::{ChainSpec, MainnetEthSpec};
+    use beacon_chain::types::MainnetEthSpec;
     use std::sync::Arc;
     use types::FixedBytesExtended;
 
@@ -400,10 +400,31 @@ mod test {
         harness.get_current_state()
     }
 
+    fn get_store<E: EthSpec>() -> HotColdDB<E, MemoryStore<E>, MemoryStore<E>> {
+        let store =
+            HotColdDB::open_ephemeral(Config::default(), Arc::new(E::default_spec())).unwrap();
+        // Init achor info so anchor slot is set. Use a random block as it is only used for the
+        // parent_root
+        let _ = store
+            .init_anchor_info(Hash256::ZERO, Slot::new(0), Slot::new(0), false)
+            .unwrap();
+        // Write a state with state root 0 which is the base `put_state` below tries to diff from
+        {
+            let harness = BeaconChainHarness::builder(E::default())
+                .default_spec()
+                .deterministic_keypairs(1)
+                .fresh_ephemeral_store()
+                .build();
+            let genesis_state = harness.get_current_state();
+            store.put_state(&Hash256::ZERO, &genesis_state).unwrap();
+        }
+        store
+    }
+
     #[test]
     fn block_root_iter() {
-        let store =
-            HotColdDB::open_ephemeral(Config::default(), Arc::new(ChainSpec::minimal())).unwrap();
+        let store = get_store::<MainnetEthSpec>();
+
         let slots_per_historical_root = MainnetEthSpec::slots_per_historical_root();
 
         let mut state_a: BeaconState<MainnetEthSpec> = get_state();
@@ -449,8 +470,8 @@ mod test {
 
     #[test]
     fn state_root_iter() {
-        let store =
-            HotColdDB::open_ephemeral(Config::default(), Arc::new(ChainSpec::minimal())).unwrap();
+        let store = get_store::<MainnetEthSpec>();
+
         let slots_per_historical_root = MainnetEthSpec::slots_per_historical_root();
 
         let mut state_a: BeaconState<MainnetEthSpec> = get_state();