math.big: add test cases for is_power_of_2

[phoreverpheebs]

🤖 Generated by Copilot at d354c9b

Add tests for big.Int.is_power_of_2 method. The tests verify the method's functionality on various positive and negative integers.

🤖 Generated by Copilot at d354c9b

• Add a constant is_power_of_2_test_data to provide test cases for the is_power_of_2 method of the big.Int type (link)
• Add a test function test_is_power_of_2 to verify the functionality and accuracy of the is_power_of_2 method of the big.Int type using the is_power_of_2_test_data constant (link)