tests: convert test_cc_power_state_change.py to pytest

[MoeSalah1999]

Proposed Commit Message

Converted test_cc_power_state_change.py from unittest to pytest:
- Removed all TestCase subclasses.
- Used pytest fixtures instead of the unittest setUp method.
- Converted all self.assert to plain assert.

Fixes GH-#6427 (GitHub Issue number. Remove line if irrelevant)

Additional Context

Test Steps

Merge type

• [x] Squash merge using "Proposed Commit Message"
• [ ] Rebase and merge unique commits. Requires commit messages per-commit each referencing the pull request number (#<PR_NUM>)