Improve argument coloring where available

[cottsay]

• Use %(default)s where appropriate
• Otherwise, use backticks around default values
• Use backticks when referring to console commands, such as references to other command line options or example command invocations

Example with Python 3.15:

Note that we're not actually choosing the palette here, we're just giving argparse the information it needs to align with other console output.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 87.66%. Comparing base (6428dca) to head (48ed3a0).

Additional details and impacted files

@@           Coverage Diff           @@
##           master     #743   +/-   ##
=======================================
  Coverage   87.66%   87.66%           
=======================================
  Files          74       74           
  Lines        4442     4442           
  Branches      771      771           
=======================================
  Hits         3894     3894           
  Misses        433      433           
  Partials      115      115           

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[PiousCrossten]

Works fine, nothing breaks. Ran the tests locally, flake8 and spell check pass, coverage unchanged.

One thing that looks like it slipped through:
verb/test.py:93 and :98 - the --build-base / --install-base args there are identical to the ones in verb/build.py (same wrap_default_value() defaults), but they still say (default: build) / (default: install). So colcon build --help gets the coloring and colcon test --help doesn't.

Rest LGTM 👍