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FLASHING.md says how to take a newer version of the colleague's tree (copy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