adding dof manager to params and re-writing params as an equinox module

[cmhamel]

This PR does two main things:

1. Re-writes Params as an equinox module so we can stash the DofManager here. This didn't work out of the box with Params as a namedtuple, hence the change. No runtime affects were encountered.
2. Keeps backwards comparability in place.

Why did I do this?

With the current setup, if you want to change Dirichlet BCs, you'd need to redefine all energy functions, etc. that implicitly use the DofManager. Now we can just create a new DofManager with the new desired BCs and update this in Params. This will of course likely lead to re-jitting whenever the DofManager changes which should at most be a handful of times even in the most complex analyses.

[codecov]

Codecov Report

Attention: Patch coverage is 80.76923% with 10 lines in your changes missing coverage. Please review.

Project coverage is 77.25%. Comparing base (fc47de4) to head (3247e1c).

Files with missing lines	Patch %	Lines
optimism/Objective.py	80.76%	10 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #111      +/-   ##
==========================================
- Coverage   77.26%   77.25%   -0.02%     
==========================================
  Files          62       62              
  Lines        5230     5267      +37     
==========================================
+ Hits         4041     4069      +28     
- Misses       1189     1198       +9     

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