(chore) handle darwing & more stringent clippy flags

[mkatychev]

Standard cargo clippy still threw unused flags due to running on macOS:

warning: constant `CAP` is never used
   --> src/lib.rs:522:11
    |
522 |     const CAP: usize = 100_000_000;
    |           ^^^
    |
    = note: `#[warn(dead_code)]` on by default

warning: function `get_rss_anon` is never used
   --> src/lib.rs:524:8
    |
524 |     fn get_rss_anon() -> usize {
    |        ^^^^^^^^^^^^

• Encapsulated linux specific function and const in particular unit test
• Handled more stringent clippy warnings dealing with compiler hints, performance, and ergonomics running: cargo clippy --all-targets --all-features -- -W clippy::uninlined_format_args -W clippy::pedantic