Remove Type Hints from CspRenderingTestCase

[andoriyaprashant]

Description

This PR removes explicit type annotations and unnecessary imports from the CspRenderingTestCase class as suggested in #2087

• Changes made:
  • Removed all type hints within the CspRenderingTestCase methods (ex - root: Element, namespaces: dict[str, str], etc.).
  • Removed unused cast, Element, and ContextList imports.
  • Preserved all logic and test behavior - only typing-related changes were made.

Fixes # 2087

Checklist:

• I have added the relevant tests for this change.
• I have added an item to the Pending section of docs/changes.rst.

[matthiask]

Slightly sad, but I have to say it looks less noisy. The annotations for basic functions look good, but cast really doesn't.