inspect_proc: capture additional memory fields to aid OOM diagnosis

[erfrimod]

Problem

inspect_proc in openhcl/underhill_core/src/inspect_proc.rs captures memory telemetry
from /proc/meminfo and per-process /proc/<pid>/status, used both for on-demand
inspection and periodic telemetry logging.

I had to investigate an OOM error recently and had to rely on the inspect_proc output. I think it would be worth collecting additional fields for future investigations. These are just a couple suggestions, maybe there are other fields that would be better?

/proc/meminfo captures 11 fields (MemTotal, MemFree, Mapped, Slab,
AnonPages, SUnreclaim, KernelStack, PageTables, Shmem, Percpu,
Committed_AS) but is missing:

Field	OOM relevance
MemAvailable	Pairs with MemTotal and MemFree.
SReclaimable	Paired with the existing SUnreclaim.
Mlocked	Memory locked via mlock() — non reclaimable memory.

/proc/<pid>/status captures 5 fields (VmSize, VmPeak, VmRSS, VmHWM,
RssAnon) but is missing:

Field	OOM relevance
RssFile	File-backed RSS (reclaimable). Completes the RSS breakdown.
RssShmem	Shared memory RSS. RssAnon + RssFile + RssShmem = VmRSS.

[smmalis37]

I have no concerns about adding these.