Parallel MCMC in tutorials

[damonbayer]

Closes #274.
Supposedly our Github runners have 4 cores, so we should be able to perform sampling in parallel. https://docs.github.com/en/actions/using-github-hosted-runners/about-github-hosted-runners/about-github-hosted-runners#standard-github-hosted-runners-for-public-repositories

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 92.80%. Comparing base (a2bd8e4) to head (9367ba3).

Additional details and impacted files

@@           Coverage Diff           @@
##             main     #278   +/-   ##
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  Coverage   92.80%   92.80%           
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  Files          40       40           
  Lines         903      903           
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  Hits          838      838           
  Misses         65       65           

Flag	Coverage Δ
unittests	92.80% <ø> (ø)

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[dylanhmorris]

LGTM. Maybe just add a note for the user about the set_host_device_count calls and how they may wish to reconfigure on their own systems.