Average value option for distance filter

[adebardo]

Once the issue #699 is closed

Context

Currently, the distance_filter function computes the local average using a Gaussian filter.
It would be useful to make this averaging method configurable to support alternative approaches, such as median filter, mean filter, or other custom kernels.

Code

• Add a new parameter, average_method: str = "gaussian", with options such as "gaussian", "median", "mean".
• Ensure consistent handling of NaN values for all methods.

Tests

Adding the necessary unit tests