feat: switch to a per-device metrics model for vsock and rng devices

[aerosouund]

Changes

Building on the original PR and addressing the reviewer comments.
With the following remarks:

• Vsock device metrics are keyed in the btreemap by the guest CID which is hardcoded for test instance to be 52. if the desire is to run the tests in a given file, it may be needed to not hardcode it
• Entropy device metrics use a random generated UUID as the key of the map, because entropy devices don't have a unique identifier in the system that distinguishes them from one another (if one exists, let me know about it)

Reason

Closes #4709

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• This functionality cannot be added in rust-vmm.