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FLASHING.md says how to take a newer version of the colleague's tree (copy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

@@ -0,0 +1,74 @@
+#ifndef A5037FF9_14E0_4DA9_8027_6C0692B1462B
+#define A5037FF9_14E0_4DA9_8027_6C0692B1462B
+
+#include <vanetza/security/hashed_id.hpp>
+#include <boost/optional/optional.hpp>
+#include <list>
+#include <unordered_map>
+
+namespace vanetza
+{
+namespace security
+{
+
+class PeerRequestTracker
+{
+public:
+    explicit PeerRequestTracker(std::size_t limit = 16);
+
+    /**
+     * Add a certificate request to the tracker.
+     * 
+     * \param id hash of requested certificate
+     */
+    void add_request(const HashedId3&);
+
+    /**
+     * Discard a pending certificate request.
+     * 
+     * \param id hash of certificate
+     */
+    void discard_request(const HashedId3&);
+
+    /**
+     * Check if a certificate request is pending.
+     * 
+     * \param id hash of certificate
+     * \return true if request of this certificate is pending
+     */
+    bool is_pending(const HashedId3&) const;
+
+    /**
+     * Determine which request shall be handled next and remove it from the queue.
+     * 
+     * \return hash of requested certificate if any
+     */
+    boost::optional<HashedId3> next_one();
+
+    /**
+     * Retrieve next n pending requests from tracker.
+     * 
+     * \return list of up to n certificate hashes
+     */
+    std::list<HashedId3> next_n(std::size_t max);
+
+    /**
+     * Retrieve all pending requests from tracker.
+     * 
+     * \return list of all pending certificate hashes
+     */
+    std::list<HashedId3> all();
+
+private:
+    using FifoQueue = std::list<HashedId3>;
+    using LookupMap = std::unordered_map<HashedId3, FifoQueue::iterator>;
+
+    std::size_t m_limit;
+    FifoQueue m_fifo;
+    LookupMap m_lookup;
+};
+
+} // namespace security
+} // namespace vanetza
+
+#endif /* A5037FF9_14E0_4DA9_8027_6C0692B1462B */