Feat: Add neighboring point search modes

Add an enum to configure how the filter selects the closest points (to calculate the PCA) to a given point according to the behavior set by SearchMode. 2 modes:

• KNN, K points (set by SampleSize) are selected regardless of their location, if Radius is also set to a value, the code checks if the farthest point found (K-th) is inside this radius. In that case, the surrounding points are reselected inside this radius.
• RADIUS, the surrounding points are selected inside the radius, if SampleSize is also set to a value, the code checks if at least SampleSize (K) points have been selected. Otherwise, SampleSize (K) points are reselected.

The previous behavior is presered thanks to the default values set in the class constructor.