fix(build): add iterate permission for test directory

Zig 0.15 requires .iterate = true flag when opening directories for iteration

Fixes panic: reached unreachable code in std.fs.Dir.iterate

cli/build.zig

@@ -171,7 +171,7 @@ pub fn build(b: *std.Build) void {
     test_step.dependOn(&run_main_tests.step);
 
     // Find all test files in tests/ directory automatically
-    var test_dir = std.fs.cwd().openDir("tests", .{}) catch |err| {
+    var test_dir = std.fs.cwd().openDir("tests", .{ .iterate = true }) catch |err| {
         std.log.warn("Failed to open tests directory: {}", .{err});
         return;
     };