Proposal: change find_germs default mode to compactEVD.

[rileyjmurray]

The find_germs function accepts a few runtime modes: {'all-Jac', 'single-Jac', 'compactEVD'}. Compact EVD runs orders of magnitudes faster than the other modes for 2-qubit germ selection. I suggest it be made the default mode, replacing the current default of all-Jac.

A counter-argument to this suggestion is that all-Jac can run with a wider range of settings than compactEVD. My counter-counter argument to that is that the defaults for other kwargs means that users can already set mode='compactEVD' without having to think beyond that. If a user provides a keyword argument that conflicts with compactEVD then it'd reasonable for us to just raise an error saying "you have to change the mode to something other than compactEVD if you want to use kwarg {k}={v}."

[coreyostrove]

I'm mostly game, though I would like to track down the issue we were seeing the other day when using compactEVD with complex data types before confidently doing so. Aside from that, now that this codepath has existed and been practically deployed for a couple of years now I think most of the possibility for really embarassing bugs/errors has been bought down so I'd be comfortable with it. There are a few other performance-related settings which we can update at the same time. Things like 'assume_real' and 'float_type', which can have their values inferred from the other inputs (the model's basis would let us know if assume_real can be set to true, for example). Since this is a nontrivial behavior change let's target this for 0.9.15.