Implement custom power and equation functions

[fevzibagriacik]

Added custom_power lambda and custom_equation function for calculations, along with fn_w_counter for tracking function calls.

Describe your changes

Checklist

• I have read the [CONTRIBUTING]
• I have performed a self-review of my own code
• I have run the code locally and it works as expected
• I have commented my code, particularly in hard-to-understand areas

Screenshots (if appropriate)