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/lightpanda.zig

@@ -108,7 +108,7 @@ pub fn fetch(app: *App, url: [:0]const u8, opts: FetchOpts) !void {
         .reason = .address_bar,
         .kind = .{ .push = null },
     });
-    _ = session.wait(opts.wait_ms, opts.wait_until);
+    _ = session.wait(.{ .timeout_ms = opts.wait_ms, .until = opts.wait_until });
 
     const writer = opts.writer orelse return;
     if (opts.dump_mode) |mode| {