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FLASHING.md says how to take a newer version of the colleague's tree (copy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

@@ -0,0 +1,40 @@
+#pragma once
+
+#include "sha.hpp"
+#include <vanetza/asn1/security/EtsiTs103097Data.h>
+#include <vanetza/common/byte_buffer.hpp>
+
+namespace vanetza
+{
+namespace pki
+{
+
+class Certificate;
+class CertificateStorage;
+class HashedId8;
+class SecurityModule;
+
+bool validate(SecurityModule&, const Vanetza_Security_EtsiTs103097Data_t&, const Certificate&);
+bool validate(SecurityModule&, const Vanetza_Security_SignedData_t&, const Vanetza_Security_Certificate_t&);
+
+// True iff the response's requestHash echoes the request: the leftmost 16 octets of the request's SHA-256
+bool check_request_hash(const Sha256Hash& request_digest, const ByteBuffer& response_hash);
+
+const Vanetza_Security_SignedData_t* get_signed_data(const Vanetza_Security_EtsiTs103097Data_t&);
+const Vanetza_Security_Opaque_t* get_unsecured_data(const Vanetza_Security_EtsiTs103097Data_t&);
+bool signed_by(SecurityModule&, const Vanetza_Security_SignedData_t&, const HashedId8&);
+HashAlgorithm get_hash_algorithm(const Vanetza_Security_SignedData_t&);
+
+template<typename Hash>
+Hash calculate_digest(SecurityModule&, const Vanetza_Security_ToBeSignedData_t&, const Vanetza_Security_Certificate_t*);
+
+template<>
+Sha256Hash calculate_digest(SecurityModule&, const Vanetza_Security_ToBeSignedData_t&,
+    const Vanetza_Security_Certificate_t*);
+
+template<>
+Sha384Hash calculate_digest(SecurityModule&, const Vanetza_Security_ToBeSignedData_t&,
+    const Vanetza_Security_Certificate_t*);
+
+} // namespace pki
+} // namespace vanetza