w: fix column widths

[cakebaker]

This PR adapts the column widths of the TTY and PCPU columns to match those of the original w.

Before the change:

$ cargo run -q w
USER     TTY      LOGIN@   IDLE   JCPU   PCPU WHAT
...

After the change:

$ cargo run -q w
USER     TTY       LOGIN@   IDLE   JCPU   PCPU  WHAT
...

Original w (I omit the first line as we don't have implemented it yet in our version):

$ w
USER     TTY       LOGIN@   IDLE   JCPU   PCPU  WHAT
...

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 0.00%. Comparing base (3ff0247) to head (ceb5213).
Report is 7 commits behind head on main.

Additional details and impacted files

@@     Coverage Diff     @@
##   main   #377   +/-   ##
===========================
===========================

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