pwdx: use usize when parsing pid, not i32

[cakebaker]

This PR uses usize instead of i32 when parsing a PID and removes an unnecessary cast.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 61.40%. Comparing base (a8b52ad) to head (2e01edd).
Report is 33 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #240      +/-   ##
==========================================
- Coverage   65.16%   61.40%   -3.76%     
==========================================
  Files          42       42              
  Lines        4415     4415              
  Branches      702      680      -22     
==========================================
- Hits         2877     2711     -166     
- Misses       1535     1546      +11     
- Partials        3      158     +155     

Flag	Coverage Δ
macos_latest	46.01% <100.00%> (-2.38%)	⬇️
ubuntu_latest	58.50% <100.00%> (-8.06%)	⬇️
windows_latest	0.06% <0.00%> (ø)

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