v0.54.0: Kaleidostrobe at 60 fps, its big window on the GPU, two-tone gray mode, sync can go sooner

The plugin still steps at its own 25 fps, frame for frame; between frames
the turn continues, textures crossfade, and the cone follows a preview of
the newest audio, so beats land a refresh sooner. The big window replays
the original's GL calls through OpenGL (QPainter took ~40 ms a frame at
1080p); without GL it falls back. Gray mode is only the gray-mode colour on
the panel background. The sync slider goes to -50 ms (sooner).

tests/test_round84.py

@@ -14,6 +14,7 @@ wave-table entry. The port has to reproduce them exactly.
 import hashlib
 import math
 from pathlib import Path
+from types import SimpleNamespace
 
 import numpy as np
 import pytest
@@ -238,7 +239,8 @@ class TestRenderer:
         for _ in range(frames):
             r.advance(_frame(dt=0.04))
         ours = _paint(r, 96, 60)
-        gl = _gl_reference(r._frame, 96, 60)
+        layers, textures = r._shown      # the in-between picture, not the frame
+        gl = _gl_reference(SimpleNamespace(layers=layers, textures=textures), 96, 60)
         assert np.abs(ours - gl).max() <= 3
 
     def test_fills_any_shape(self, qapp):
@@ -250,14 +252,6 @@ class TestRenderer:
             magenta = (img[..., 0] == 255) & (img[..., 1] == 0) & (img[..., 2] == 255)
             assert not magenta.any()        # the cone reaches every corner
 
-    def test_dim_mode_is_gray(self, qapp):
-        r = KaleidostrobeRenderer()
-        for _ in range(5):
-            r.advance(_frame(dt=0.04))
-        r.dimmed = True                     # the widget then passes its gray
-        img = _paint(r, 120, 80, color="gray")
-        assert np.abs(img[..., 0] - img[..., 2]).max() <= 2   # gray tint
-
     def test_pause_blanks_but_keeps_the_plugin(self, qapp):
         r = KaleidostrobeRenderer()
         for _ in range(5):