Compile lookaround regex to avoid compiling each time we want to use it

main.go

@@ -469,6 +469,8 @@ func thompson(re []postfixNode) *State {
 							state.assert = NLB
 						}
 					}
+					tmpRe := shuntingYard(state.lookaroundRegex)
+					state.lookaroundNFA = thompson(tmpRe)
 
 				}
 			}