UI: drop dvui fork pin — native EditorFrameTiming in Studio

Description

Replace the dvui-fork timing dependency with a native studio/EditorFrameTiming.zig that uses nanoTime brackets around Studio's existing frame calls (win.begin → addAllEvents → widgets → win.endRendering → win.end), reproducing all four FrameTiming fields. Point studio/ProfilerPanel.zig:184-192 at it. Re-pin build.zig.zon to upstream david-vanderson/dvui main.