Updating to compatability with new Turing Major versions

[odunbar]

Purpose

• Closes Suddenly MCMC can't find step size "Failed to choose suitable stepsize in 20 iterations." -> Quick temporary Fix inside #387

Content

• Update compatability (primarily around how the MCMC chains are now initialized
• Update compats, which are no longer back compatible: For future information, the minimal working version is:

AbstractMCMC v5.10.0
AdvancedMH v0.8.7
ForwardDiff v1.3.0
GaussianProcesses v0.12.6
MCMCChains v7.6.0

---

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

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 94.09%. Comparing base (5fdb164) to head (f2c9c5a).
⚠️ Report is 1 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #388      +/-   ##
==========================================
- Coverage   94.15%   94.09%   -0.06%     
==========================================
  Files          10       10              
  Lines        1624     1625       +1     
==========================================
  Hits         1529     1529              
- Misses         95       96       +1     

☔ View full report in Codecov by Sentry.
📢 Have feedback on the report? Share it here.

🚀 New features to boost your workflow:

• ❄️ Test Analytics: Detect flaky tests, report on failures, and find test suite problems.

[odunbar]

Applying merge without review as tests all passing and coverage maintained