Issue #442: Generalise to all brms distributions

[seabbs]

Description

This PR closes #442. It adds function factories and uses primarycensored to generalise the latent model to all brms supported distributions.

My outstanding uncertainty here is the naming and organisation of these functions. It would also be nice to still support custom families but I think that might need to be a new issue/stretch goal (as is quite edge case functionality anyway).

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[seabbs]

@kylieainslie I think this PR has put us in a place where we can think about testing mixtures using the brms mixture() family (which I think should now nearly "just work" with the double censoring and truncation methods in the latent model generalised here. I am not sure but I think what it would need is a custom family for convolution mixture components (i.e 2 * lognormal, and so on) and then be good to go.

[codecov]

Codecov Report

Attention: Patch coverage is 97.77778% with 1 line in your changes missing coverage. Please review.

Project coverage is 93.93%. Comparing base (e840b4b) to head (cca651b).
Report is 7 commits behind head on main.

Files with missing lines	Patch %	Lines
R/latent_model.R	95.65%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #459      +/-   ##
==========================================
- Coverage   94.24%   93.93%   -0.31%     
==========================================
  Files          16       14       -2     
  Lines         469      429      -40     
==========================================
- Hits          442      403      -39     
+ Misses         27       26       -1     

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[seabbs]

The coverage gap we see here is not a new gap but showing up due to copying the function into a new location. In general the log likelihood tests are a bit weak but its also really hard to test. A potentially sensible candidate for a mocked test sometimes in the future

[athowes]

🥳