Update all .cpp files to use .cc extension (google style)

pipeline/src/data_generation/mock/generate_user.cc

@@ -0,0 +1,22 @@
+/**
+ * @file data_generation/mock/generate_user.cc
+ * @brief Generates deterministic mock user profiles by hashing locale values
+ * into predefined username and bio collections.
+ */
+
+#include <functional>
+#include <string>
+#include <string_view>
+
+#include "data_generation/mock_generator.h"
+
+UserResult MockGenerator::GenerateUser(const std::string& locale) {
+  const std::size_t hash = std::hash<std::string>{}(locale);
+
+  UserResult result;
+  const std::string_view username = kUsernames[hash % kUsernames.size()];
+  const std::string_view bio = kBios[hash / 11 % kBios.size()];
+  result.username = username;
+  result.bio = bio;
+  return result;
+}