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/src/client/config.rs

@@ -152,7 +152,7 @@ impl Default for ClientConfig {
 }
 #[cfg(test)]
 mod test {
-	use super::{DatabaseCompactionProfile, Mode};
+	use super::{DatabaseCompactionProfile};
 
 	#[test]
 	fn test_default_compaction_profile() {