Bugfix parameter name bug for MV distributions, cap mac-os tests to julia v1.9.0

[odunbar]

Purpose

MCMCChains requires one name per dimension for MCMC diagnostics. This causes an error when Multivariate distributions are used. This PR fixes this bug.

Content

• uses the dimension of prior distribution in MCMC to clone the name e.g. a 3D "u" -> ["u_1","u_2","u_3"]
• adds a quick unit-test for a case where #names < #prior dimensions

Misc

• using sqrt(C) * MVNormal(0,I) instead of MVNormal(0,C)
• for an unknown reason, the Mac tests with v1.9.1 onwards are hanging on the package build of CES, so capping at v1.9.0

---

• I have read and checked the items on the review checklist.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Comparison is base (a621a04) 88.09% compared to head (e991cbe) 88.05%.
Report is 14 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #277      +/-   ##
==========================================
- Coverage   88.09%   88.05%   -0.05%     
==========================================
  Files           7        8       +1     
  Lines        1134     1172      +38     
==========================================
+ Hits          999     1032      +33     
- Misses        135      140       +5     

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[odunbar]

Small bugfixes with unit tests, and buildkite passing with unchanged results.