Add cosine channel for MPCD

[tzortziskoul]

Description

We want to implement a second channel for mpcd streaming geometry in hoomd v4. It will be a symmetric wavy channel.

Proposed solution

The new geometry will be implemented as follows:

channel = hoomd.mpcd.geometry.CosineChannel(...)
hoomd.mpcd.stream.BounceBack(period=..., geometry=channel)

Additional context

We already have a plugin that implements some of the necessary infrastructure for hoomd v2, which we will port to hoomd v4. A similar issue has been opened for assymetric Contraction Expansion channel.

[mphoward]

This issue is very similar to #1775 but the two cosines follow each other to make an S-shaped geometry. We will support implementing this feature too.

My only comment is that this geometry should be named CosineChannel according to our discussion, not CosineWavy.

[tzortziskoul]

Yes, this is right, I just changed it to CosineChannel.

[mphoward]

Completed in #1836