A last bunch of txqueue performance optimizations (#9024)

* Clear cache only when block is enacted.

* Add tracing for cull.

* Cull split.

* Cull after creating pending block.

* Add constant, remove sync::read tracing.

* Reset debug.

* Remove excessive tracing.

* Use struct for NonceCache.

* Fix build

* Remove warnings.

* Fix build again.

ethcore/sync/src/api.rs

@@ -384,7 +384,6 @@ impl NetworkProtocolHandler for SyncProtocolHandler {
 	}
 
 	fn read(&self, io: &NetworkContext, peer: &PeerId, packet_id: u8, data: &[u8]) {
-		trace_time!("sync::read");
 		ChainSync::dispatch_packet(&self.sync, &mut NetSyncIo::new(io, &*self.chain, &*self.snapshot_service, &self.overlay), *peer, packet_id, data);
 	}