Premshaw04/#7713/ICAR wrapper should return MvNormal.dist instead of constructing the RV directly

[premshaw04]

Description

Related Issue

• [*] Closes Add rng_fn to CAR/ICAR #7713
• Related to #

Checklist

• [*] Checked that the pre-commit linting/style checks pass
• [*] Included tests that prove the fix is effective or that the new feature works
• Added necessary documentation (docstrings and/or example notebooks)
• If you are a pro: each commit corresponds to a relevant logical change

Type of change

• [*] New feature / enhancement
• Bug fix
• [] Documentation
• Maintenance
• Other (please specify):

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📚 Documentation preview 📚: https://pymc--7955.org.readthedocs.build/en/7955/

[premshaw04]

please pre-commit.ci autofix