rename our packages & repo

[landinjm]

We ought to rename the packages to be something more descriptive. While we're at it, the repo should be renamed. The IPAM2025 part is redundant.

[j-fu]

• IonConservingModifiedPoissonBoltzmann would be ideally descriptive but is too lon.
• IonConstrainedPoisson shorter and catchier, refers to both ion number and ion size constraints. Would need some explanation but points in the right direction. My favorite so far including compared to the suggestions of ChatGPT and DeepSeek.