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FLASHING.md says how to take a newer version of the colleague's tree (copy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

@@ -0,0 +1,20 @@
+#include "signed_data.hpp"
+#include <vanetza/asn1/security/Ieee1609Dot2Content.h>
+
+namespace vanetza
+{
+namespace pki
+{
+
+void SignedData::move_into(Vanetza_Security_Ieee1609Dot2Data_t& dest) &&
+{
+    auto* self = content();
+    // Release anything dest already held (normally none) to avoid leaks.
+    ASN_STRUCT_FREE(asn_DEF_Vanetza_Security_Ieee1609Dot2Content, dest.content);
+    dest.protocolVersion = self->protocolVersion;
+    dest.content = self->content;
+    self->content = nullptr;
+}
+
+} // namespace pki
+} // namespace vanetza