cmd, consensus, core, miner: instatx clique for --dev (#15323)

* cmd, consensus, core, miner: instatx clique for --dev

* cmd, consensus, clique: support configurable --dev block times

* cmd, core: allow --dev to use persistent storage too

miner/worker.go

@@ -269,6 +269,11 @@ func (self *worker) update() {
 
 				self.current.commitTransactions(self.mux, txset, self.chain, self.coinbase)
 				self.currentMu.Unlock()
+			} else {
+				// If we're mining, but nothing is being processed, wake on new transactions
+				if self.config.Clique != nil && self.config.Clique.Period == 0 {
+					self.commitNewWork()
+				}
 			}
 
 		// System stopped