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/dcc/tests/burst_budget.cpp

@@ -0,0 +1,63 @@
+#include <gtest/gtest.h>
+#include <vanetza/common/manual_runtime.hpp>
+#include <vanetza/dcc/burst_budget.hpp>
+
+using Runtime = vanetza::ManualRuntime;
+using namespace vanetza::dcc;
+
+static const vanetza::Clock::duration immediately = std::chrono::milliseconds(0);
+
+TEST(BurstBudget, normal)
+{
+    Runtime rt;
+    BurstBudget budget(rt);
+
+    // consume whole budget
+    for (unsigned i = 0; i < 20; ++i) {
+        rt.trigger(std::chrono::milliseconds(49));
+        EXPECT_EQ(immediately, budget.delay());
+        budget.notify();
+    }
+
+    // nothing left now
+    rt.trigger(std::chrono::milliseconds(20));
+    EXPECT_LT(std::chrono::seconds(9), budget.delay());
+    EXPECT_GT(std::chrono::seconds(10), budget.delay());
+}
+
+TEST(BurstBudget, too_many_messages)
+{
+    Runtime rt;
+    BurstBudget budget(rt);
+
+    // consume whole budget immediately
+    for (unsigned i = 0; i < 20; ++i) {
+        EXPECT_EQ(immediately, budget.delay());
+        budget.notify();
+    }
+
+    // check if budget delay recovers gradually
+    EXPECT_EQ(std::chrono::seconds(10), budget.delay());
+    rt.trigger(std::chrono::seconds(5));
+    EXPECT_EQ(std::chrono::seconds(5), budget.delay());
+    rt.trigger(std::chrono::seconds(5));
+    EXPECT_EQ(immediately, budget.delay());
+}
+
+TEST(BurstBudget, too_long)
+{
+    Runtime rt;
+    BurstBudget budget(rt);
+
+    // start burst with one consumption
+    EXPECT_EQ(immediately, budget.delay());
+    budget.notify();
+
+    // ensure we are still able to participate in burst
+    rt.trigger(std::chrono::milliseconds(990));
+    EXPECT_EQ(immediately, budget.delay());
+
+    // burst is over, we will have to wait for next one
+    rt.trigger(std::chrono::milliseconds(10));
+    EXPECT_EQ(std::chrono::seconds(9), budget.delay());
+}