feat(distributions): support symbolic eta in LKJCholeskyCov logp

[sankhyanreyansh]

Description

This PR allows the eta parameter in pm.LKJCholeskyCov to be a symbolic/dynamic PyTensor variable (e.g., placing a prior such as pm.HalfNormal on eta), bringing it to feature parity with LKJCorr.logp.

• Removes the try...except NotScalarConstantError restriction on eta in _LKJCholeksyCovRV_logp.
• Preserves the scalar constant check for n (since static matrix dimensioning is required by PyTensor shape indexing).
• Updates the relevant TODO in pymc/distributions/multivariate.py.
• Adds unit tests in tests/distributions/test_multivariate.py verifying finite logp and dlogp evaluations with symbolic eta, as well as validating that non-constant n still raises NotImplementedError.

Related Issue

• Closes Support symbolic eta parameter in LKJCholeskyCov.logp #8403

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):

[read-the-docs-community]

Documentation build overview

📚 pymc | 🛠️ Build #34172782 | 📁 Comparing 5a39fbd against latest (da8fc47)

  🔍 Preview build  

3 files changed

± glossary.html
± _modules/pymc/distributions/multivariate.html
± _modules/pytensor/tensor/extra_ops.html

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 91.88%. Comparing base (47bdf54) to head (5a39fbd).
⚠️ Report is 1 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #8404   +/-   ##
=======================================
  Coverage   91.87%   91.88%           
=======================================
  Files         128      128           
  Lines       21256    21253    -3     
=======================================
- Hits        19530    19529    -1     
+ Misses       1726     1724    -2     

Files with missing lines	Coverage Δ
pymc/distributions/multivariate.py	95.58% <ø> (+0.20%)	⬆️

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