- Add class-level caches for loader and default RAM/NVRAM values
- When multiple IOU nodes use the same image, only the first one runs
the ld-linux --verify and iou-image -h subprocesses
- Subsequent nodes reuse cached results, saving ~2 subprocess calls per node
- Cache is populated only on successful subprocess execution to avoid
overwriting explicitly set ram/nvram values with stale cached defaults
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