w: truncate long username

[Bluemangoo]

my username is bluemangoo

cargo run -q w
 16:57:30 up  7:06,  4 users,  load average: 1.48, 1.07, 0.96
USER     TTY       LOGIN@   IDLE   JCPU   PCPU  WHAT
bluemang tty1      09:51    7:06m  0.05   0.05  /usr/bin/startplasma-wayland
bluemang pts/0     09:51    7:06m  8241.887.48  /usr/bin/kded5
bluemang pts/2     16:28    28:05  0.48   0.4   /usr/bin/zsh
bluemang pts/3     16:28    28:38  0.25   0.17  /usr/bin/zsh

fix #438

[Bluemangoo]

fixed.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 0.00%. Comparing base (2318b27) to head (89c55bb).
⚠️ Report is 108 commits behind head on main.

Additional details and impacted files

@@     Coverage Diff     @@
##   main   #454   +/-   ##
===========================
===========================

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