GPU fix:
- Revert to CUDA_VISIBLE_DEVICES approach but with lazy CuPy init
- gpu.py: CuPy is no longer imported at module level; _init_gpu()
imports it lazily on first to_gpu() call. This allows workers to
set CUDA_VISIBLE_DEVICES before CuPy creates a CUDA context.
- gpu.py: detect GPU count via nvidia-smi (no CUDA context needed)
- pipeline.py: each worker sets CUDA_VISIBLE_DEVICES=N before CuPy
init, so each process uses only its assigned GPU
Rendering improvements:
- Title: split into bold title (14pt) + italic description (10pt)
instead of single 15pt bold block
- North arrow: moved inside data area (top-right corner) with
semi-transparent white background for readability over data
- Colorbar: full height (no gap for compass rose), added
ScalarFormatter(useOffset=False) to avoid scientific notation
- Colorbar compass rose gap removed since north arrow is now
inside the data area
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