Implement Scan based filter helper

[emekaokoli19]

Description

This PR adds a filter helper function to pytensor/scan/views.py, complementing the existing map, reduce, foldl, and foldr utilities.

The new filter function applies a user-defined condition (predicate) over a sequence using PyTensor’s scan operation and returns only the elements that satisfy the condition (i.e., the ones for which the predicate evaluates to True).

This addition restores functionality discussed in Theano/Theano#5365, now updated for PyTensor where boolean indexing is supported natively.

A corresponding unit test (test_filter) was added in tests/scan/test_views.py to ensure correct behavior.

Related Issue

• Closes Add filter to scan/views.py #1711

Checklist

• Checked that pre-commit linting/style checks pass
• Included a test (test_filter) that verifies the correctness of the new function
• Added necessary documentation (docstring for filter)
• Each commit corresponds to a relevant logical change

Type of change

• New feature / enhancement

@ricardoV94, please take a look when available

[ricardoV94]

Looks great, just some small suggestions/request

[emekaokoli19]

@ricardoV94 I have addressed the reviews. Also, is there a Discord or Slack community for Pytensor I can join? Thank you.

[ricardoV94]

Thanks @emekaokoli19 looks great.

There's a discord but only available to recurring developers. If you contribute a while longer you'll be invited. Otherwise we prefer to keep discussion public and easy to find here on Github with issues/discussions.