Allow for the potential_fn to be a Callable

[michaeldeistler]

We now only require that the potential_fn takes theta and x_o as inputs.

def potential(theta, x_o):
    return sim.log_prob(theta, x_o) + prior.log_prob(theta)


posterior = MCMCPosterior(
    potential_fn=potential,
    proposal=posterior.set_default_x(x_o),
)
samples = posterior.sample((100,), x=x_o)

The newly added tests take 2.14 seconds in total.

Closes #765

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Comparison is base (3b1f34e) 75.29% compared to head (db89fc7) 75.94%.
Report is 3 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #943      +/-   ##
==========================================
+ Coverage   75.29%   75.94%   +0.65%     
==========================================
  Files          80       80              
  Lines        6285     6306      +21     
==========================================
+ Hits         4732     4789      +57     
+ Misses       1553     1517      -36     

Flag	Coverage Δ
unittests	75.94% <100.00%> (+0.65%)	⬆️

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[janfb]

Looks great, thanks! Good idea to use a wrapper here.

I added a couple of questions regarding documentation and making sure the passed potential has what we need.

[janfb]

Great! Just one final comment about the typing.

[janfb]

looks good and ready to go into main. Thanks!