various: fix clippy warnings

- Adds proper documentation comments with `# Errors` sections for all
  functions returning `Result`
- `cast_precision_loss` on `u64` -> `f64` for disk sizes is acceptable
  since disk sizes won't exceed f64's precision limit in practice.
  Thus, we can suppress those.
- `cast_sign_loss` and `cast_possible_truncation` on the percentage
  calculation is safe since percentages are always 0-100. Once again,
  it's safe to suppress.

Signed-off-by: NotAShelf <raf@notashelf.dev>
Change-Id: Id4dd7ebc9674407d2be4f38ff4de24bc6a6a6964

src/uptime.rs

@@ -1,5 +1,10 @@
 use std::{fmt::Write, io, mem::MaybeUninit};
 
+/// Gets the current system uptime.
+///
+/// # Errors
+///
+/// Returns an error if the system uptime cannot be retrieved.
 #[cfg_attr(feature = "hotpath", hotpath::measure)]
 pub fn get_current() -> Result<String, io::Error> {
   let uptime_seconds = {
@@ -7,6 +12,7 @@ pub fn get_current() -> Result<String, io::Error> {
     if unsafe { libc::sysinfo(info.as_mut_ptr()) } != 0 {
       return Err(io::Error::last_os_error());
     }
+    #[allow(clippy::cast_sign_loss)]
     unsafe { info.assume_init().uptime as u64 }
   };