Dev/rosenblatttransform (#241)

- added rosenblatttransform 
- added 3x3 eta methods 
- interpolation can be used with various eta functions
- added documentation for interpolation, eta calculation 
- exposed full eta struct in python 
- disable ClusterFinder for 2x2 clusters 
- factory function for ClusterVector

---------

Co-authored-by: Dhanya Thattil <dhanya.thattil@psi.ch>
Co-authored-by: Erik Fröjdh <erik.frojdh@psi.ch>

include/aare/algorithm.hpp

@@ -109,4 +109,19 @@ template <typename Container> bool all_equal(const Container &c) {
     return false;
 }
 
+/**
+ * linear interpolation
+ * @param bin_edge left and right bin edges
+ * @param bin_values function values at bin edges
+ * @param coord coordinate to interpolate at
+ * @return interpolated value at coord
+ */
+inline double linear_interpolation(const std::pair<double, double> &bin_edge,
+                                   const std::pair<double, double> &bin_values,
+                                   const double coord) {
+    const double bin_width = bin_edge.second - bin_edge.first;
+    return bin_values.first * (1 - (coord - bin_edge.first) / bin_width) +
+           bin_values.second * (coord - bin_edge.first) / bin_width;
+}
+
 } // namespace aare