Format Problem XBlock Files in edx-platform #436

Description:

Apply consistent formatting across all Problem XBlock–related files in edx-platform to match the style used in xblocks-contrib/problem.

This ensures minimal diffs when extracting the block later.

Tasks:

• Format Python files using black and isort
• Format CSS, JS, and YAML files using prettier.
• Fix pylint warnings and errors

Acceptance Criteria:

• No functional changes
• Code formatting matches xblocks-contrib conventions
• All CI checks pass