test: increase test coverage for mantle_map_converter_utils

Added positive and negative test cases for the uncovered code in mantle-map_converter_utils.

RoadLogicSuite/Internal/MapConversion/BUILD

@@ -135,3 +135,13 @@ cc_test(
         "@googletest//:gtest_main",
     ],
 )
+
+cc_test(
+    name = "mantle_map_converter_utils_test",
+    timeout = "short",
+    srcs = ["mantle_map_converter_utils_test.cpp"],
+    deps = [
+        ":mantle_map_converter_utils",
+        "@googletest//:gtest_main",
+    ],
+)
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