Try to address WPT running OOM

- Continue to reuse the Browser/Env/Isolate, but no start a new session per test.
- Test http server now properly closes the sendFile fd
- Run WPT in ReleaseMode
- Add --quiet option to WPT and some commented out debug code for dumping v8
  memory stats

src/TestHTTPServer.zig

@@ -74,6 +74,7 @@ pub fn sendFile(req: *std.http.Server.Request, file_path: []const u8) !void {
         error.FileNotFound => return req.respond("server error", .{ .status = .not_found }),
         else => return err,
     };
+    defer file.close();
 
     const stat = try file.stat();
     var send_buffer: [4096]u8 = undefined;