Merge parent and current sync lookups (#5655)

* Drop lookup type trait for a simple arg

* Drop reconstructed for processing

* Send parent blocks one by one

* Merge current and parent lookups

* Merge current and parent lookups clean up todos

* Merge current and parent lookups tests

* Merge remote-tracking branch 'origin/unstable' into sync-merged-lookup

* Merge branch 'unstable' of https://github.com/sigp/lighthouse into sync-merged-lookup

* fix compile after merge

* #5655 pr review (#26)

* fix compile after merge

* remove todos, fix typos etc

* fix compile

* stable rng

* delete TODO and unfilled out test

* make download result a struct

* enums instead of bools as params

* fix comment

* Various fixes

* Track ignored child components

* Track dropped lookup reason as metric

* fix test

* add comment describing behavior of avail check error

*  update ordering

common/lru_cache/src/time.rs

@@ -166,6 +166,12 @@ where
         self.map.contains(key)
     }
 
+    /// List known keys
+    pub fn keys(&mut self) -> impl Iterator<Item = &Key> {
+        self.update();
+        self.map.iter()
+    }
+
     /// Shrink the mappings to fit the current size.
     pub fn shrink_to_fit(&mut self) {
         self.map.shrink_to_fit();