[VM] Retain bytecode modules for rodata refs

Bytecode rodata buffers are embedded in their owning module and may be retained by HAL imports or other external refs after VM context teardown has begun. Requiring queue resource cleanup before completion would put arbitrary release work on latency-sensitive signal paths.

Represent module-storage buffers explicitly: initialize them with zero external refs, retain the storage module on the first external buffer retain, and release it when the last external ref drops. This keeps the archive storage alive for late releases without moving resource destruction onto queue completion.