Fixed the get_var func

[prajwalun]

Description

This PR fixes and improves the get_var_by_name utility function:

• Removes the unused ids parameter.
• Adds a new include_inner_graphs flag (default: False) to control whether variables from inner graphs (e.g., inside Scan, FunctionGraph, etc.) are included in the search.
• Updates the docstring for clarity and accurate parameter documentation.
• Adds a dedicated test to verify that inner graph variables are only returned when include_inner_graphs=True.

This behavior aligns with issue #1440 and ensures graph traversal behaves in a more predictable and scoped manner by default.

Related Issue

• Closes Tweak get_var_by_name #1440
• 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)
• 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://pytensor--1441.org.readthedocs.build/en/1441/

[ricardoV94]

Looks great

[ricardoV94]

Some related test is failing: https://github.com/pymc-devs/pytensor/actions/runs/15456457168/job/43525580655?pr=1441#step:6:2199