Improve page.wait

Allow page.wait to transition page mode.

Optimize initial page load. No point running scheduler until the initial
page is loaded.

Support ISO-8859-1 charset

src/testing.zig

@@ -408,6 +408,7 @@ pub const JsRunner = struct {
 
         const html_doc = try parser.documentHTMLParseFromStr(opts.html);
         try page.setDocument(html_doc);
+        page.mode = .{ .parsed = {} };
 
         return .{
             .app = app,