Add clear command

src/builtin/cmds/clear.zig

@@ -0,0 +1,10 @@
+const std = @import("std");
+
+const types = @import("../types.zig");
+
+pub fn execute(ctx: types.CommandContext) !void {
+    try ctx.stdout.writeStreamingAll(
+        ctx.io,
+        "\x1b[2J\x1b[H",
+    );
+}