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FLASHING.md says how to take a newer version of the colleague's tree (copy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

@@ -0,0 +1,54 @@
+#ifndef RUNTIME_HPP_KHDIEMRN
+#define RUNTIME_HPP_KHDIEMRN
+
+#include <vanetza/common/clock.hpp>
+#include <functional>
+
+namespace vanetza
+{
+
+/**
+ * Runtime provides current time and enables scheduling of tasks for later execution.
+ *
+ * All calls to Runtime and objects using the same Runtime have to be invoked from same thread!
+ **/
+class Runtime
+{
+public:
+    using Callback = std::function<void(Clock::time_point)>;
+
+    /**
+     * Schedule callback for later invocation
+     * \param tp invoke callback at this time point
+     * \param cb callback
+     * \param scope associated scope pointer (used only for identification)
+     */
+    virtual void schedule(Clock::time_point tp, const Callback& cb, const void* scope = nullptr) = 0;
+
+    /**
+     * Schedule callback for later invocation
+     * \param d duration from now until callback invocation
+     * \param cb callback
+     * \param scope associated scope pointer (used only for identification)
+     */
+    virtual void schedule(Clock::duration d, const Callback& cb, const void* scope = nullptr) = 0;
+
+    /**
+     * Cancel all scheduled invocations assigned to certain scope
+     * \param scope any pointer used as scope at scheduling (nullptr has no effect)
+     */
+    virtual void cancel(const void* scope) = 0;
+
+    /**
+     * Get current time
+     * \return current time
+     */
+    virtual Clock::time_point now() const = 0;
+
+    virtual ~Runtime() = default;
+};
+
+} // namespace vanetza
+
+#endif /* RUNTIME_HPP_KHDIEMRN */
+