Fix MP4 memory usage and remove cmcrameri-dependent colormaps

Stream MP4 frames incrementally via imageio.get_writer instead of
loading all frames into memory at once with mimwrite (OOM risk for
long videos). Remove berlin/managua/vanimo from the interactive
colormap list — these require the optional cmcrameri package and
silently fail without it.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

Author: sbryngelson

toolchain/mfc/viz/interactive.py

@@ -28,8 +28,7 @@
     "Blues", "Greens", "Oranges", "Reds", "Purples", "Greys",
     "twilight", "twilight_shifted", "hsv",
     "tab10", "tab20", "terrain", "ocean", "gist_earth",
-    "gnuplot", "gnuplot2", "CMRmap", "cubehelix",
-    "berlin", "managua", "vanimo", "Wistia",
+    "gnuplot", "gnuplot2", "CMRmap", "cubehelix", "Wistia",
 ]
 
 # ---------------------------------------------------------------------------

toolchain/mfc/viz/renderer.py

@@ -374,12 +374,12 @@ def render_mp4(varname, steps, output, fps=10,  # pylint: disable=too-many-argum
 
     success = False
     try:
-        imageio.mimwrite(
-            output,
-            [imageio.imread(os.path.join(viz_dir, fname)) for fname in frame_files],
-            fps=fps, codec='libx264', pixelformat='yuv420p', macro_block_size=2,
-            ffmpeg_log_level='error',
-        )
+        with imageio.get_writer(
+            output, fps=fps, codec='libx264', pixelformat='yuv420p',
+            macro_block_size=2, ffmpeg_log_level='error',
+        ) as writer:
+            for fname in frame_files:
+                writer.append_data(imageio.imread(os.path.join(viz_dir, fname)))
         success = True
     except (OSError, ValueError, RuntimeError) as exc:
         print(f"imageio MP4 write failed: {exc}")