Update Eigen to 5.0.0

[WardBrian]

Eigen 5.0.0 was recently released https://gitlab.com/libeigen/eigen/-/releases/5.0.0

Note: They also changed their release naming conventions from WORLD.MAJOR.MINOR to MAJOR.MINOR.PATCH, so this is much closer to a "Eigen 3.5.0" by the old naming scheme than initially appears

[WardBrian]

One thing to do after this is update our fft functions, as Eigen now has more options including sometimes having a 2d FFT that would be much faster than our current loop