Add CircuitCombiner class for flexible QPIXL integration with an input circuit

[NazTM]

Fixes #3
Addressing the current limitations due to hardcoded integrations within the given cFRQI_with_alg_demo function, this PR includes a function to combine QPIXL-encoded image circuits with quantum algorithm circuits.

Changes:

1. Refactored cFRQI_with_alg_demo to only return the FRQI image encoding circuit.
2. Introduced a new CircuitCombiner class with support for sequential mode, merge mode and a custom mode for interleaving control.
3. Included driver code demonstrating the application all three modes (sequential, merge, custom) in the notebook.
4. Updated markdown cells to explain both the modified function and the newly introduced class.

[danielbultrini]

Thank you! I will compare the implementations tomorrow, I was on vacation until today, hence why I didn't manage to update you until today.