Validate system shared memory region size when registering a region

[rmccorm4]

This PR:

• Validate System SHM region size during registration
• Add system shm registration tests

Deferred to separate PRs:

• Validate CUDA SHM region size
  • need to investigate the right way to query device pointer allocated size from cuIPC handle
• Validate System SHM file/user permissions
  • need a test to validate the existing code would fail with bad permissions when container is setup with a non-root user (ex: shm_open)

ref: DLIS-6198

[rmccorm4]

Added tests for system shm registration to L0_shared_memory.

• Tests fail locally before server-side changes, and pass after server-side changes ✅

[nnshah1]

LGTM

[nnshah1]

@rmccorm4 , @fpetrini15

Small, non blocking items:

I also thought while reading that GetSharedMemoryRegionSize was more intuitive than Info as we weren't getting more information. At the moment - I'm hoping permissions are checked when we actual do the map for reading / writing and don't need to be checked independently. If we do have to do more checks we could update it then. Also the comment says metadata, maybe GetSharedMemoryRegionMetadata ?

Another small tweak could be to wrap the validation into a function: CheckRegionSize()

struct stat sb -> struct stat file_status?

sb wasn't immediately clear to me - it's not used very much

These are all minor - and non blocking.

[fpetrini15]

TM,LG! 🚀