approval-voting: populate session cache in advance (#3954)

* try populating session cache in advance

* remove unused arg

* fmt

* fix compilation

* fix tests

* Revert "fix tests"

This reverts commit e8222b1108e09a39727a38e3b4e4c3061642a213.

* fix tests

* bump dispute window const by 1

* fix tests

polkadot/node/primitives/src/lib.rs

@@ -69,7 +69,8 @@ pub const POV_BOMB_LIMIT: usize = (MAX_POV_SIZE * 4u32) as usize;
 /// On Polkadot this is 1 day, and on Kusama it's 6 hours.
 ///
 /// Number of sessions we want to consider in disputes.
-pub const DISPUTE_WINDOW: SessionIndex = 6;
+/// + 1 for the child's session.
+pub const DISPUTE_WINDOW: SessionIndex = 6 + 1;
 
 /// The cumulative weight of a block in a fork-choice rule.
 pub type BlockWeight = u32;