Tweak wait_until option

Small tweaks to https://github.com/lightpanda-io/browser/pull/1896

Improve the wait ergonomics with an Option with default parameter. Revert
page pointer logic to original (don't think that change was necessary).

src/main_legacy_test.zig

@@ -106,7 +106,7 @@ pub fn run(allocator: Allocator, file: []const u8, session: *lp.Session) !void {
     defer try_catch.deinit();
 
     try page.navigate(url, .{});
-    _ = session.wait(2000, .load);
+    _ = session.wait(.{});
 
     ls.local.eval("testing.assertOk()", "testing.assertOk()") catch |err| {
         const caught = try_catch.caughtOrError(allocator, err);