MSRV for procfs

The `procfs` crate currently has a MSRV of 1.48, and this is verified via CI checks. However, it is increasingly difficult to actually test on 1.48 because more and more of the rust ecosystem will arbitrary change their MSRV (even in patch versions).

Our CI script is [full of cargo pins](https://github.com/eminence/procfs/blob/9a4e8672bd8cdc87376b5a2ad868fe537a817f0c/.github/workflows/rust.yml#L29-L46) to keep certain dependencies on older versions.

I am now strongly considering changing the MSRV of rust to be something way less conservative. I'm not sure exactly what it should be If anyone has any thoughts, please let me know

Start with the pinned dependency ranges in .github/workflows/rust.yml, especially lines 29–46, and review how the current Rust 1.48 MSRV is verified in CI. The issue needs a decided replacement MSRV before work can be considered done, followed by updating the CI pins and checks to match it.

Written by the indexing model from the issue text.