Implemented algorithms for K-Nearest Neighbor Search (KNN)

[lucaderi]

Please sign (check) the below before submitting the Pull Request:

• [ X] I have signed the ntop Contributor License Agreement at https://github.com/ntop/legal/blob/main/individual-contributor-licence-agreement.md
• [X ] I have read the contributing guidelines at https://github.com/ntop/nDPI/blob/dev/CONTRIBUTING.md
• [ X] I have updated the documentation (in doc/) to reflect the changes made (if applicable)

Describe changes:
Implemented the following API new calls:

  ndpi_kd_tree* ndpi_kd_create(u_int num_dimensions);
  void ndpi_kd_free(ndpi_kd_tree *tree);
  void ndpi_kd_clear(ndpi_kd_tree *tree);
  bool ndpi_kd_insert(ndpi_kd_tree *tree, const double *data_vector, void *user_data);
  ndpi_kd_tree_result *ndpi_kd_nearest(ndpi_kd_tree *tree, const double *data_vector);
  u_int32_t ndpi_kd_num_results(ndpi_kd_tree_result *res);
  double* ndpi_kd_result_get_item(ndpi_kd_tree_result *res, double **user_data);
  void ndpi_kd_result_free(ndpi_kd_tree_result *res);
  double ndpi_kd_distance(double *a1, double *b2, u_int num_dimensions);

   ndpi_btree* ndpi_btree_init(double **data, u_int32_t n_rows, u_int32_t n_columns);
   ndpi_knn ndpi_btree_query(ndpi_btree *b, double **query_data,
                            u_int32_t query_data_num_rows, u_int32_t query_data_num_columns,
                            u_int32_t max_num_results);
   void ndpi_free_knn(ndpi_knn knn);
   void ndpi_free_btree(ndpi_btree *tree);

[sonarqubecloud]

Quality Gate passed

Issues
0 New issues
0 Accepted issues

Measures
0 Security Hotspots
0.0% Coverage on New Code
0.0% Duplication on New Code

See analysis details on SonarCloud