Keep vanetza-idf in obu-firmware, so a plain clone builds the firmware

obu-firmware builds against the vanetza-idf C-ITS library, which until now
came from the colleague's microbu-esp32c5 tree beside the repository and was
not tracked here, so a clone of this repository could not build the firmware
it ships. The library alone is now part of obu-firmware, as
obu-firmware/external/vanetza-idf: their external/vanetza-idf at commit
cf4b99f, unchanged (9775 files; see its PROVENANCE.md). CMake takes it from
there by default; -DVANETZA_IDF_DIR still points the build elsewhere.

The rest of the colleague's tree (their own VAM firmware, PKI tooling,
station-link Python tools, the V2X2MAP bridge) stays out of this repository
and gitignored; nothing is pushed to their repository. NOTES.md, docs/06,
TODO.md and the pcap verifier's usage line point at the new location.

obu-firmware/external/vanetza-idf/vanetza/geodesy/tests/m49_code.cpp

@@ -0,0 +1,39 @@
+#include <vanetza/geodesy/m49_code.hpp>
+#include <gtest/gtest.h>
+#include <map>
+#include <string>
+#include <unordered_set>
+
+using vanetza::geodesy::M49Code;
+
+TEST(M49Code, value)
+{
+    M49Code code(276);
+    EXPECT_EQ(276, code.value());
+}
+
+TEST(M49Code, equality)
+{
+    EXPECT_EQ(M49Code(276), M49Code(276));
+    EXPECT_NE(M49Code(276), M49Code(250));
+}
+
+TEST(M49Code, std_hash)
+{
+    std::unordered_set<M49Code> codes;
+    codes.insert(M49Code(276));
+    codes.insert(M49Code(250));
+    codes.insert(M49Code(276)); // duplicate
+    EXPECT_EQ(2u, codes.size());
+    EXPECT_EQ(1u, codes.count(M49Code(276)));
+    EXPECT_EQ(1u, codes.count(M49Code(250)));
+}
+
+TEST(M49Code, std_less)
+{
+    std::map<M49Code, std::string> names;
+    names[M49Code(276)] = "Germany";
+    names[M49Code(250)] = "France";
+    EXPECT_EQ("Germany", names.at(M49Code(276)));
+    EXPECT_EQ("France", names.at(M49Code(250)));
+}