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 #
• Related to Code cleanups #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):