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.hpp

@@ -0,0 +1,44 @@
+#pragma once
+#include <boost/asio/io_context.hpp>
+#include <boost/asio/steady_timer.hpp>
+#include <kj/async.h>
+#include <kj/timer.h>
+#include <atomic>
+
+namespace vanetza
+{
+namespace rpc
+{
+
+class AsioEventPort : public kj::EventPort
+{
+public:
+    AsioEventPort(boost::asio::io_context& io);
+
+    bool wait() override;
+    bool poll() override;
+    void setRunnable(bool runnable) override;
+
+    void setLoop(kj::EventLoop* loop)
+    {
+        loop_.store(loop, std::memory_order_release);
+    }
+
+    kj::Timer& getTimer()
+    {
+        return timer_;
+    }
+
+private:
+    void advanceTime();
+    void armTimeout();
+
+    boost::asio::io_context& io_;
+    boost::asio::steady_timer steady_timer_;
+    std::atomic<kj::EventLoop*> loop_ { nullptr };
+    const kj::MonotonicClock& clock_;
+    kj::TimerImpl timer_;
+};
+
+} // namespace rpc
+} // namespace vanetza