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/beacon_chain/src/summaries_dag.rs

@@ -3,6 +3,7 @@ use std::{
     cmp::Ordering,
     collections::{btree_map::Entry, BTreeMap, HashMap},
 };
+use store::HotStateSummary;
 use types::{Hash256, Slot};
 
 #[derive(Debug, Clone, Copy)]
@@ -57,6 +58,12 @@ pub enum Error {
         root_state_root: Hash256,
         root_state_slot: Slot,
     },
+    CircularAncestorChain {
+        state_root: Hash256,
+        previous_state_root: Hash256,
+        slot: Slot,
+        last_slot: Slot,
+    },
 }
 
 impl StateSummariesDAG {
@@ -311,10 +318,24 @@ impl StateSummariesDAG {
         }
 
         let mut ancestors = vec![];
+        let mut last_slot = None;
         loop {
             if let Some(summary) = self.state_summaries_by_state_root.get(&state_root) {
+                // Detect cycles, including the case where `previous_state_root == state_root`.
+                if let Some(last_slot) = last_slot {
+                    if summary.slot >= last_slot {
+                        return Err(Error::CircularAncestorChain {
+                            state_root,
+                            previous_state_root: summary.previous_state_root,
+                            slot: summary.slot,
+                            last_slot,
+                        });
+                    }
+                }
+
                 ancestors.push((state_root, summary.slot));
-                state_root = summary.previous_state_root
+                last_slot = Some(summary.slot);
+                state_root = summary.previous_state_root;
             } else {
                 return Ok(ancestors);
             }
@@ -336,6 +357,17 @@ impl StateSummariesDAG {
     }
 }
 
+impl From<HotStateSummary> for DAGStateSummary {
+    fn from(value: HotStateSummary) -> Self {
+        Self {
+            slot: value.slot,
+            latest_block_root: value.latest_block_root,
+            latest_block_slot: value.latest_block_slot,
+            previous_state_root: value.previous_state_root,
+        }
+    }
+}
+
 #[cfg(test)]
 mod tests {
     use super::{DAGStateSummaryV22, Error, StateSummariesDAG};