Add ECCENTRIC trajectories

[Daval-G]

This MR adds the ECCENTRIC trajectories with 2D and 3D versions, based on the work from Klauser et al. "ECCENTRIC: a fast and unrestrained approach for high-resolution in vivo metabolic imaging at ultra-high field MR". Imaging Neuroscience 2 (2024): 1-20. and listed in #106.

It simply consists of identical circular shots distributed over the k-space and stacked spherically, as opposed to other works like concentric rings.

Here are the 2D (left, middle) and 3D (right) versions. The middle image shows the starting points distribution for each shot along with the center of each circle. The paper doesn't specify clearly how to orientate the circles so I assumed the starting points should be closest to the center, as further described in the docstring notes.

TODO:

• Add gallery example in 2D
• Add gallery example in 3D