User customizable name_transform

[BrianPugh]

This PR primarily adds two new fields: App.name_transform and Parameter.name_transform. The function's responsibility is to convert python identifiers to their CLI counterparts and has signature:

def name_transform(s: str) -> str:
    ...

These name transforms can be set at a global level for your app:

app = App(
    name_transform=lambda name: name,  # don't modify the name at all. This applies to command names.
    default_parameter=Parameter(name_transform=lambda name: name),  # This applies to parameter names.
)

They can also be set in individual subapps (subapps inherit name_transform from their parent), or in individual Annotated[...., Parameter(name_transform=my_custom_transform)] definitions.

Addresses #140.

[codecov-commenter]

Codecov Report

Attention: Patch coverage is 98.38710% with 1 lines in your changes are missing coverage. Please review.

Project coverage is 96.24%. Comparing base (f87ea85) to head (b19224c).

Files	Patch %	Lines
cyclopts/_convert.py	96.15%	1 Missing ⚠️

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Additional details and impacted files

@@            Coverage Diff             @@
##             main     #150      +/-   ##
==========================================
+ Coverage   96.19%   96.24%   +0.05%     
==========================================
  Files          16       16              
  Lines        1789     1813      +24     
  Branches      453      458       +5     
==========================================
+ Hits         1721     1745      +24     
  Misses         31       31              
  Partials       37       37              

Flag	Coverage Δ
unittests	96.02% <98.38%> (+0.05%)	⬆️

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