fix(testgen): distinguish between C and C++ based on file extension

Update language detection in testgen to set "C++" for files with .cpp, .cc, .cxx extensions, and "C" otherwise when the language is specified as "C/C++".

cmd/testgen.go

@@ -50,6 +50,15 @@ Examples:
 				continue
 			}
 			lang := langObj.Name
+			if lang == "C/C++" {
+				ext := strings.ToLower(filepath.Ext(filePath))
+				switch ext {
+				case ".cpp", ".cc", ".cxx":
+					lang = "C++"
+				default:
+					lang = "C"
+				}
+			}
 			if !supportedLangs[lang] {
 				color.Yellow("Unsupported lang '%s' for %s (supported: Go/Python/C/C++)", lang, filePath)
 				allSuccess = false