refactor(uucore): integrate procfs for Linux memory parsing

[mattsu2020]

Summary

• add a Linux-only procfs dependency to query /proc/meminfo via safe APIs
• reuse procfs::Meminfo to compute total and available memory bytes for uucore parsers
• expose parse_size_non_zero_u64 so callers can reject zero-sized inputs consistently

Testing

• cargo check --workspace

[github-actions]

GNU testsuite comparison:

Skipping an intermittent issue tests/misc/tee (passes in this run but fails in the 'main' branch)
Skipping an intermittent issue tests/tail/overlay-headers (passes in this run but fails in the 'main' branch)
Skipping an intermittent issue tests/timeout/timeout (passes in this run but fails in the 'main' branch)

[Alonely0]

Is there something wrong with our implementation, or more places where we would want to use this crate? I'd rather avoid adding new dependencies if we can do it ourselves, especially such a large one for just parsing one file; I do not think the supply-chain attack risks outweigh the maintainability benefits in this case.

EDIT: Seems you already discussed this with Sylvestre, so I'll shut up :). However, I'd prefer if you took a peak at how they do it, implemented it in that way (or similarly, such that we get what we're after) and then credit them properly in a copyright comment. I still have strong feelings about adding a crate of thousands of LOC for a parser of 20 lines :/

[github-actions]

GNU testsuite comparison:

Skip an intermittent issue tests/tail/overlay-headers (fails in this run but passes in the 'main' branch)
Skip an intermittent issue tests/timeout/timeout (fails in this run but passes in the 'main' branch)
Skipping an intermittent issue tests/misc/tee (passes in this run but fails in the 'main' branch)

[sylvestre]

@Alonely0 this ship has sailed a long time ago :)
Happy to have a longer explanation of the why if you want

[Alonely0]

@Alonely0 this ship has sailed a long time ago :) Happy to have a longer explanation of the why if you want

I'd love to get more acquainted on uutils' policy on dependencies and how it has come to be :)

[sylvestre]

it isn't complex : i am lazy! :)

More seriously, one of the reason why I think Rust is successful is cargo and its ecosystem!

Using crate, even for "simple" things like this one allows better cross collaboration, you don't have to reinvent the wheel and you benefit from the future evolution of the crate almost of free.
If ever there is a security issue on the function (unlikely, i agree), we would be notified by using the crate. Probably not if we forked it
Here, if we would have forked this functions, we would have to update it for clippy new warnings, adjust for potential kernel changes, etc