Simplify flag handling in qvm_ls

[hippalectryon-0]

Purpose

qvm_ls has a huge chunk of code dedicated to handling flags - that appears to be remnant of an old, mostly unused implementation.

This PR greatly simplifies this logic by transforming flags into just another standard Column.
This PR shouldn't change any user-facing feature.

Minor changes

• Light reformatting / cleanup of Columns
• Add new utests

[codecov]

Codecov Report

❌ Patch coverage is 70.00000% with 12 lines in your changes missing coverage. Please review.
✅ Project coverage is 76.36%. Comparing base (1a623d1) to head (fd70a12).

Files with missing lines	Patch %	Lines
qubesadmin/tools/qvm_ls.py	70.00%	12 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #447      +/-   ##
==========================================
+ Coverage   76.24%   76.36%   +0.11%     
==========================================
  Files          53       53              
  Lines        9322     9282      -40     
==========================================
- Hits         7108     7088      -20     
+ Misses       2214     2194      -20     

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