Fix bug when `freezing_rv_and_dims` after a model transformation

[ricardoV94]

Description

Also adds optimization to avoid cloning the fgraph when it will be discarded anyway. Benchmarked with long models and can cut clone_model (the simplest workflow) by 2x

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
• [x] Bug fix
• [ ] Documentation
• [ ] Maintenance
• [ ] Other (please specify):

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📚 Documentation preview 📚: https://pymc--7296.org.readthedocs.build/en/7296/