Keep the colleague's microbu-esp32c5 tree in this repository

obu-firmware builds against vanetza-idf from microbu-esp32c5/external, but
that tree was gitignored, so a clone of this repository could not build the
firmware it ships. It is now committed here as ordinary files in its own
folder, microbu-esp32c5/: the colleague's commit cf4b99f plus the V2X2MAP
bridge's signature verification (--trust) used on the bench. Nothing is
fetched from or pushed to the colleague's repository; this repository and
its remotes carry everything. The folder's own .gitignore keeps build output,
downloaded components and private key material out, as it did there; the
committed file set is identical to that repository's tracked files.

The ESP32-C5 is still flashed from obu-firmware/, which only takes
vanetza-idf from microbu-esp32c5/, so the two stay separate folders.
FLASHING.md says how to take a newer version of the colleague's tree (copy
it over the folder, rebuild, test, commit).

microbu-esp32c5/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