Remove the custom frozendict implementation

[Armavica]

Description

Spin off from #842 aiming to remove the custom frozendict implementation.

Although it might be the case one day, there is currently no frozendict implementation in Python. A few libraries offer this, and we vendored one implementation (wrapper over a dict object). We only use it in the attributes of the Elemwise object. It might be beneficial to remove this custom object and replace it with a built-in Python immutable container (like a tuple). However, this makes a test fail: tests_kanren:test_KanrenRelationSub_filters, more details here.

Related Issue

• [ ] Closes #
• [x] Related to #842

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):