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/state_machine_budget.cpp

@@ -0,0 +1,40 @@
+#include <vanetza/common/runtime.hpp>
+#include <vanetza/dcc/state_machine.hpp>
+#include <vanetza/dcc/state_machine_budget.hpp>
+
+namespace vanetza
+{
+namespace dcc
+{
+
+StateMachineBudget::StateMachineBudget(const StateMachine& fsm, const Runtime& rt) :
+    m_fsm(fsm), m_runtime(rt)
+{
+}
+
+Clock::duration StateMachineBudget::delay()
+{
+    Clock::duration delay = Clock::duration::max();
+
+    if (m_last_tx) {
+        const auto last_tx = m_last_tx.get();
+        const auto tx_interval = m_fsm.transmission_interval();
+        if (last_tx + tx_interval < m_runtime.now()) {
+            delay = Clock::duration::zero();
+        } else {
+            delay = last_tx + tx_interval - m_runtime.now();
+        }
+    } else {
+        delay = Clock::duration::zero();
+    }
+
+    return delay;
+}
+
+void StateMachineBudget::notify()
+{
+    m_last_tx = m_runtime.now();
+}
+
+} // namespace dcc
+} // namespace vanetza