[onert] Improve model type inference with filesystem path handling (#16258)

This commit updates inferModelType function to accept filesystem::path directly and handle extension in a case-insensitive way.
It updates load_model_from_path function to use inferModelType.

ONE-DCO-1.0-Signed-off-by: Hyeongseok Oh <hseok82.oh@samsung.com>

Author: hseok-oh

runtime/onert/api/nnfw/src/Session.cc

@@ -33,6 +33,8 @@
 
 #include <misc/string_helpers.h>
 
+#include <algorithm>
+#include <cctype>
 #include <fstream>
 #include <iostream>
 #include <string>
@@ -113,11 +115,15 @@ std::string trim(std::string_view value)
   return std::string(value.substr(begin, end - begin + 1));
 }
 
-std::string inferModelType(const std::string &filename)
+std::string inferModelType(const std::filesystem::path &file_path)
 {
-  std::filesystem::path file_path(filename);
-  std::string ext = file_path.extension().string();
-  return ext.empty() ? "" : ext.substr(1);
+  if (!file_path.has_extension())
+    return "";
+
+  auto type = file_path.extension().string().substr(1);
+  std::transform(type.begin(), type.end(), type.begin(),
+                 [](unsigned char c) { return std::tolower(c); });
+  return type;
 }
 
 bool loadConfigure(const std::string cfgfile, onert::util::CfgKeyValues &keyValues)
@@ -332,10 +338,17 @@ NNFW_STATUS Session::load_model_from_path(const char *path)
   try
   {
     std::filesystem::path filename{path};
-    if (!std::filesystem::is_directory(filename) && filename.has_extension())
+    if (!std::filesystem::is_directory(filename))
     {
-      std::string model_type = filename.extension().string().substr(1); // + 1 to exclude dot
-      return loadModelFile(filename, model_type);
+      std::string model_type = inferModelType(filename);
+      if (model_type.empty())
+      {
+        std::cerr << "Error: Cannot determine model type for '" << filename << "'."
+                  << "Please use a file with valid extension." << std::endl;
+        return NNFW_STATUS_ERROR;
+      }
+      else
+        return loadModelFile(filename, model_type);
     }
 
     const auto &package_dir = filename;
@@ -386,14 +399,15 @@ NNFW_STATUS Session::load_model_from_path(const char *path)
 
     for (uint16_t i = 0; i < num_models; ++i)
     {
-      const auto model_file_path = package_dir / models[i].asString();
+      const auto model_file_name = std::filesystem::path(models[i].asString());
+      const auto model_file_path = package_dir / model_file_name;
       std::string model_type;
 
       // Use model-types if available and not empty, otherwise infer from file extension
       if (!model_types.empty() && i < model_types.size())
         model_type = model_types[i].asString();
       else
-        model_type = inferModelType(models[i].asString());
+        model_type = inferModelType(model_file_name);
       if (model_type.empty())
       {
         std::cerr << "Error: Cannot determine model type for '" << models[i].asString() << "'."