Add HalfNormalRV JAX implementation

[theorashid]

This for #1335. The distribution does not exist exactly in jax.random, but it can be easily transformed. I chose loc + jax.random.truncated_normal(rng_key, 0.0, jax.numpy.inf, size, dtype) * scale, but you could equally choose loc + jax.numpy.abs(jax.random.normal(rng_key, size, dtype)) * scale. It's up to the maintainers to decide which they prefer. The tests work but I'm happy to implement more tests if desired.

Might also need to consider key splitting order #1345.

Side note: I'm more familiar with the numpyro/tfp-style HalfNormal distributions, which have a single scale parameter are centred at zero.

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[rlouf]

This looks good! Waiting for #1345 to be merged. In the meantime, would you mind rebasing your changes and renaming the commit to match the PR title?

[theorashid]

I rebased and changed the split key to match #1345.

[rlouf]

I cleaned the commits; should be good to merge if the tests pass. Thank you for contributing!

[codecov]

Codecov Report

Merging #1362 (e0b8fb1) into main (94f3f32) will increase coverage by 0.00%.
The diff coverage is 100.00%.

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #1362   +/-   ##
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  Coverage   74.35%   74.36%           
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  Files         177      177           
  Lines       49056    49066   +10     
  Branches    10379    10379           
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+ Hits        36478    36488   +10     
  Misses      10285    10285           
  Partials     2293     2293           

Impacted Files	Coverage Δ
aesara/link/jax/dispatch/random.py	100.00% <100.00%> (ø)