Add Support for Multiple Antennas

[kimbank]

I have made modifications to add support for multiple antennas. The original code only supported single antennas, which limited its applicability for more advanced setups with multiple antennas.

Changes Made:

• Modified the interpolate method in read_feitcsi.py to handle multiple antennas by iterating over the third dimension (tx index) in the CSI matrix.
• Updated the interpolation logic for both amplitude and phase to accommodate multiple antennas.
• Ensured backward compatibility with the original single antenna setup.

Testing:

• Verified the changes with both single and multiple antenna setups.
• Ensured that the interpolation results are correct and consistent across different configurations.

Feel free to modify the message to better fit your needs or to add any additional details.