Fix shm_dir location in cache structure

Dan Notesteinrequested to merge
fix/shm-dir-cache-structure into develop

Cache was incorrectly storing shm_dir inside datadir, but runtime expects them as siblings.

Fixed:

  1. Save cache templates now copy datadir and shm_dir as siblings (matching HAF cache structure)
  2. Smart cache lookup moves shm_dir if found inside datadir (backward compatible with old caches)

This fixes the sync job failing with 'no such file or directory' when Docker tries to mount shm_dir.

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