Improve CLI Test Suite for open_data_pvnet

[SophiaLi20]

This PR cleans up and improves the test suite for the open_data_pvnet CLI. The goal is to make the tests more readable, maintainable, and robust, while also covering a few missing edge cases.
What’s Changed?

• Refactored Repetitive Code
• Made Tests Easier to Read
• Covered More Edge Cases
• Better Mocks, More Reliable Tests

Why this change matter?
This makes the test suite cleaner, easier to maintain, and ready for future updates. It also ensures we don’t miss edge cases that could cause unexpected failures.

Checklist:

• My code follows OCF's coding style guidelines
• I have performed a self-review of my own code
• No breaking changes introduced
• I have added tests that prove my fix is effective or that my feature works
• I have checked my code and corrected any misspellings