fix: improve help(f3d)

[carsonRadtke]

Describe your changes

• Removes the CMake stub from the help message
• Removes the private exported constants from the help message
• Adds all the pyf3d exports to the help message

Issue ticket number and link if any

Fixes: https://github.com/f3d-app/f3d/issues/1019

Checklist for finalizing the PR

• [x] I have performed a self-review of my code
• [ ] I have added tests for new features and bugfixes
• [ ] I have added documentation for new features
• [ ] If it is a modifying the libf3d API, I have updated bindings
• [ ] If it is a modifying the .github/workflows/versions.json, I have updated timestamp

Continuous integration

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[carsonRadtke]

The new help message looks like: f3d.help.txt

[Meakk]

@snoyer can you take a look?

[mwestphal]

It definitely looks much better, but indeed needs a @snoyer review :)

[mwestphal]

@carsonRadtke please push again, I've enabled CI :)