Avoid spurious deprecation warning in CustomDist

Description

The warning is causing the CI in pymc-experimental to fail https://github.com/pymc-devs/pymc-experimental/pull/352

Also allow multivariate CustomDist to be created when signature suffices to infer core shape.

Related Issue

[ ] Closes #
[ ] 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):

📚 Documentation preview 📚: https://pymc--7391.org.readthedocs.build/en/7391/

Codecov Report

All modified and coverable lines are covered by tests :white_check_mark:

Project coverage is 92.19%. Comparing base (b496127) to head (b2f3c48). Report is 83 commits behind head on main.

Additional details and impacted files

[![Impacted file tree graph](https://app.codecov.io/gh/pymc-devs/pymc/pull/7391/graphs/tree.svg?width=650&height=150&src=pr&token=JFuXtOJ4Cb&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=pymc-devs)](https://app.codecov.io/gh/pymc-devs/pymc/pull/7391?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=pymc-devs) ```diff @@ Coverage Diff @@ ## main #7391 +/- ## ======================================= Coverage 92.19% 92.19% ======================================= Files 103 103 Lines 17214 17208 -6 ======================================= - Hits 15870 15865 -5 + Misses 1344 1343 -1 ``` | [Files with missing lines](https://app.codecov.io/gh/pymc-devs/pymc/pull/7391?dropdown=coverage&src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=pymc-devs) | Coverage Δ | | |---|---|---| | [pymc/distributions/custom.py](https://app.codecov.io/gh/pymc-devs/pymc/pull/7391?src=pr&el=tree&filepath=pymc%2Fdistributions%2Fcustom.py&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=pymc-devs#diff-cHltYy9kaXN0cmlidXRpb25zL2N1c3RvbS5weQ==) | `95.54% <100.00%> (+1.08%)` | :arrow_up: | ... and [1 file with indirect coverage changes](https://app.codecov.io/gh/pymc-devs/pymc/pull/7391/indirect-changes?src=pr&el=tree-more&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=pymc-devs)

pymc-devs / pymc