Change over to using command runner for arg parsing

lib/day1/command.dart

@@ -0,0 +1,21 @@
+import "package:args/command_runner.dart";
+
+class Day1Command extends Command {
+  // The [name] and [description] properties must be defined by every
+  // subclass.
+  final name = "day1";
+  final description = "Run Advent of Code 2025 Day 1";
+
+  Day1Command() {
+    // we can add command specific arguments here.
+    // [argParser] is automatically created by the parent class.
+  }
+
+  // [run] may also return a Future.
+  @override
+  void run() {
+    // [argResults] is set before [run()] is called and contains the flags/options
+    // passed to this command.
+    print(argResults?.rest);
+  }
+}