Misc fixes : Synthetic plotting, windowing and padding arguments fixes, forward example.

[thurinj]

I am combing through some of the open issues to try to address them.

Addressing issues:

This small PR has no major theme be covers issues:

• Problem with add_padding is True. #344
• User-provided parameters not properly set in ProcessData #334
• kwargs are not actually passed in the matplotlib beachball plotting routine #317 -> **kwarg support for savefig added to the waveform plot.
• Feature Request: Custom synthetic line colors in waveform plots #316 -> Added support for modifying both the beachball color and synthetic colors with **kwargs: color and syn_color:

this one being generated with following arguments:

beachball_color='red', dat_kwargs={'color': 'gray'}, syn_kwargs={'color': 'blue', 'linestyle': '--'}

This particular fix took some cues from PR #331 that has never been finalized.

Other changes:

I also took the liberty to update the way we discover entry point by replacing use pkg_resources which was locking us into setuptools<82, the code now use importlib.metadata's entry_points. This does not modify behaviors, but will remove deprecation warning when using setup.py:

UserWarning: pkg_resources is deprecated as an API. 
See https://setuptools.pypa.io/en/latest/pkg_resources.html. 
The pkg_resources package is slated for removal as early as 2025-11-30. 
Refrain from using this package or pin to Setuptools<81.

I also added a new dedicated example for the forward evaluation to address the following issue:

• example for direct evaluation of an input moment tensor #315 -> added a forward evaluation example.

It follow more or less the example script that was provided by @rmodrak in the issue's discussion, with its associated code generator and documentation entry.

[thurinj]

If merged, will close and cancel pending PR #331 which would become redundant.

Staged merge for the end of the week if no comments.