Unfreeze help_flags and version_flags; create/delete commands on set/get

[BrianPugh]

@PythonNinja this should fix #126 . I'll add more specific instructions in that issue.

This PR does the following:

1. Unfreezes the help_flags and version_flags attributes.
2. Creates/deletes the corresponding commands on set/del.
3. The meta app's default help_flags and version_flags now come from its parent.

[codecov-commenter]

Codecov Report

Attention: Patch coverage is 88.88889% with 3 lines in your changes are missing coverage. Please review.

Project coverage is 96.17%. Comparing base (f95622b) to head (e90f870).

Files	Patch %	Lines
cyclopts/core.py	88.88%	1 Missing and 2 partials ⚠️

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Additional details and impacted files

@@            Coverage Diff             @@
##             main     #127      +/-   ##
==========================================
- Coverage   96.30%   96.17%   -0.13%     
==========================================
  Files          16       16              
  Lines        1757     1780      +23     
  Branches      443      451       +8     
==========================================
+ Hits         1692     1712      +20     
- Misses         30       31       +1     
- Partials       35       37       +2     

Flag	Coverage Δ
unittests	96.01% <88.88%> (-0.12%)	⬇️

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[BrianPugh]

There's an independent issue (but also experienced by your example) where:

python my_script.py --verbose foo --help

erroneously displays the "root" help page instead of the help page for the foo command. I'll see if I can quickly tackle that in another PR.

[pythoninja]

There's an independent issue (but also experienced by your example) where:

python my_script.py --verbose foo --help

erroneously displays the "root" help page instead of the help page for the foo command. I'll see if I can quickly tackle that in another PR.

Yes, thank you for quick fixes.