tool: add support for measuring runtime of a program

tool/src/main/kotlin/gay/pizza/pork/tool/RunCommand.kt

@@ -7,16 +7,29 @@ import com.github.ajalt.clikt.parameters.options.option
 import com.github.ajalt.clikt.parameters.types.path
 import gay.pizza.pork.evaluator.CallableFunction
 import gay.pizza.pork.evaluator.Scope
+import kotlin.system.measureTimeMillis
 
 class RunCommand : CliktCommand(help = "Run Program", name = "run") {
   val loop by option("--loop", help = "Loop Program").flag()
+  val measure by option("--measure", help = "Measure Time").flag()
   val path by argument("file").path(mustExist = true, canBeDir = false)
 
   override fun run() {
     if (loop) {
       while (true) {
+        runProgramMaybeMeasure()
+      }
+    } else {
+      runProgramMaybeMeasure()
+    }
+  }
+
+  private fun runProgramMaybeMeasure() {
+    if (measure) {
+      val time = measureTimeMillis {
         runProgramOnce()
       }
+      println("time taken: $time ms")
     } else {
       runProgramOnce()
     }