feat: Rename `TargettedPixelGroup` to `TargetedPixelGroup`

[munechika-koyo]

Key changes:

• Rename TargettedPixelGroup to TargetedPixelGroup and add deprecation warnings.

• Remove unnecessary blank lines for improved code formatting.

[skuba31]

I have only one minor point regarding the deprecation warning. Should an explicit version number be added to the message? And if so, should it be 2.0 or a different one?

[munechika-koyo]

@skuba31 Thanks for your feedback! I specified the version number when we will remove the deprecated API.

[jacklovell]

2.0 is the appropriate place to remove deprecations, agreed. Have you checked if there are any public attributes or methods in classes which use the new Targeted spelling? For subclasses of Raysect Targeted* classes these may be present, in which case you should also add aliased methods in the compatibility class.

I wouldn't want to go too far down this rabbit hole though. We can do what we can to provide backwards compatibility, but users will find stuff breaks anyway if they use any of the Raysect classes directly so it'll never be a completely clean switch.

[Mateasek]

Also, could you please make an issue about removing the deprecated TargettedPixelGroup when we move to Cherab 2.0 version? I created a new milestone for the version 2.0, please link it with the issue so we don't forget all the deprecated code to be removed.

[Mateasek]

Thank you for adding the record into documentation and for creating the issue.

Also, thank you very much for the PR @munechika-koyo, I'm merging this into development.