add GTest infrastructure and port first mathematical tests from Java

- Add Google Test via CMake FetchContent (v1.14.0)
- Add clausen.hpp: Clausen integral, Lobachevsky function, Im(Li2)
- Add hyper_ideal_utility.hpp: generalized and ideal-vertex hyperbolic
  tetrahedron volume formulas using Eigen for the 4x4 Gram determinant
- Port ClausenTest (5 tests) and HyperIdealUtilityTest (8 tests) from
  Java/JUnit — all 13 pass with same tolerances as the Java originals
- Fix pre-existing VIEWER/viewer case mismatch in CMakeLists.txt

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

code/src/apps/v0/conformallab_cli.cpp

@@ -2,6 +2,7 @@
 #include <CGAL/Surface_mesh.h>
 #include <CGAL/IO/polygon_mesh_io.h>
 
+
 #include "viewer_utils.h"
 #include "mesh_utils.hpp"
 
@@ -34,7 +35,6 @@ bool parse_arguments(int argc, char* argv[], std::string& input_file, std::strin
     } catch (const CLI::ParseError &e) {
         return false;
     }
-    return true;
 
     if (input_file.empty()) {
         std::cerr << "Input file is required.\n";
@@ -45,12 +45,18 @@ bool parse_arguments(int argc, char* argv[], std::string& input_file, std::strin
         std::cerr << "Unsupported file format. Please provide an OFF file.\n";
         return EXIT_FAILURE;
     }
+
+    std::cout << "Input file: " << input_file << "\n";
+    std::cout << "Output file: " << output_file << "\n";
+    std::cout << "Show mesh: " << (show ? "Yes" : "No") << "\n";
+    std::cout << "Verbose: " << (verbose ? "Yes" : "No") << "\n";
+
+
+
+    return true;
 }
 
 
-
-
-
 int main(int argc, char* argv[])
 {
     std::string input_file;
@@ -63,17 +69,15 @@ int main(int argc, char* argv[])
         return EXIT_FAILURE;
     }
 
-    std::cout << "Input file: " << input_file << "\n";
-    std::cout << "Output file: " << output_file << "\n";
-    std::cout << "Show mesh: " << (show ? "Yes" : "No") << "\n";
-    std::cout << "Verbose: " << (verbose ? "Yes" : "No") << "\n";
-
     Mesh surface_mesh;
     if (!CGAL::IO::read_polygon_mesh(input_file, surface_mesh) || surface_mesh.is_empty()) {
         std::cerr << "Invalid input file: " << input_file << "\n";
         return EXIT_FAILURE;
     }
   
+
+
+    
     // #TODO: later: here we would call the unwrapping code, e.g.:
     // UnwrapSettings settings;
     // settings.target_geometry = TargetGeometry::Euclidean;