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FLASHING.md says how to take a newer version of the colleague's tree (copy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/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