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FLASHING.md says how to take a newer version of the colleague's tree (copy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

@@ -0,0 +1,81 @@
+#include <vanetza/security/hashed_id.hpp>
+#include <boost/functional/hash.hpp>
+#include <algorithm>
+#include <cassert>
+#include <iomanip>
+#include <sstream>
+
+namespace vanetza
+{
+namespace security
+{
+
+HashedId3 truncate(const HashedId8& in)
+{
+    HashedId3 out;
+    assert(out.size() <= in.size());
+    std::copy_n(in.rbegin(), out.size(), out.rbegin());
+    return out;
+}
+
+HashedId8 create_hashed_id8(const Sha256Digest& digest)
+{
+    HashedId8 hashed;
+    std::copy(digest.end() - 8, digest.end(), hashed.data());
+    return hashed;
+}
+
+HashedId8 create_hashed_id8(const Sha384Digest& digest)
+{
+    HashedId8 hashed;
+    std::copy(digest.end() - 8, digest.end(), hashed.data());
+    return hashed;
+}
+
+std::string to_string(const vanetza::security::HashedId3& digest)
+{
+  std::stringstream ss;
+  ss << std::hex << std::setfill('0');
+  for (uint8_t octet : digest)
+  {
+    ss << std::setw(2) << static_cast<unsigned>(octet);
+  }
+  return ss.str();
+}
+
+std::string to_string(const vanetza::security::HashedId8& digest)
+{
+  std::stringstream ss;
+  ss << std::hex << std::setfill('0');
+  for (uint8_t octet : digest)
+  {
+    ss << std::setw(2) << static_cast<unsigned>(octet);
+  }
+  return ss.str();
+}
+
+} // namespace security
+} // namespace vanetza
+
+namespace std
+{
+
+size_t hash<vanetza::security::HashedId3>::operator()(const vanetza::security::HashedId3& hid3) const
+{
+    size_t seed = 0;
+    for (uint8_t octet : hid3) {
+        boost::hash_combine(seed, octet);
+    }
+    return seed;
+}
+
+size_t hash<vanetza::security::HashedId8>::operator()(const vanetza::security::HashedId8& hid8) const
+{
+    size_t seed = 0;
+    for (uint8_t octet : hid8) {
+        boost::hash_combine(seed, octet);
+    }
+    return seed;
+}
+
+} // namespace std