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/rpc/asio_event_port.cpp

@@ -0,0 +1,71 @@
+#include "vanetza/rpc/asio_event_port.hpp"
+
+#include <boost/asio/post.hpp>
+#include <chrono>
+
+namespace vanetza
+{
+namespace rpc
+{
+
+AsioEventPort::AsioEventPort(boost::asio::io_context& io) :
+    io_(io),
+    steady_timer_(io_),
+    clock_(kj::systemPreciseMonotonicClock()),
+    timer_(clock_.now())
+{
+}
+
+bool AsioEventPort::wait()
+{
+    io_.run_one();
+    advanceTime();
+    armTimeout();
+    return false;
+}
+
+bool AsioEventPort::poll()
+{
+    io_.poll();
+    advanceTime();
+    armTimeout();
+    return false;
+}
+
+void AsioEventPort::setRunnable(bool runnable)
+{
+    if (runnable) {
+        boost::asio::post(io_, [this]() {
+            auto* loop = loop_.load(std::memory_order_acquire);
+            if (loop && loop->isRunnable()) {
+                loop->run();
+            }
+        });
+    }
+}
+
+void AsioEventPort::advanceTime()
+{
+    timer_.advanceTo(clock_.now());
+}
+
+void AsioEventPort::armTimeout()
+{
+    std::chrono::nanoseconds dt {
+      timer_.timeoutToNextEvent(clock_.now(), kj::NANOSECONDS, kj::maxValue)
+          .map([](uint64_t ns) { return ns; })
+          .orDefault(0)
+    };
+    if (dt > std::chrono::nanoseconds::zero()) {
+        steady_timer_.expires_after(dt);
+        steady_timer_.async_wait([this](const boost::system::error_code& ec) {
+            if (!ec) {
+                advanceTime();
+                armTimeout();
+            }
+        });
+    }
+}
+
+} // namespace rpc
+} // namespace vanetza