Keep vanetza-idf in obu-firmware, so a plain clone builds the firmware

obu-firmware builds against the vanetza-idf C-ITS library, which until now
came from the colleague's microbu-esp32c5 tree beside the repository and was
not tracked here, so a clone of this repository could not build the firmware
it ships. The library alone is now part of obu-firmware, as
obu-firmware/external/vanetza-idf: their external/vanetza-idf at commit
cf4b99f, unchanged (9775 files; see its PROVENANCE.md). CMake takes it from
there by default; -DVANETZA_IDF_DIR still points the build elsewhere.

The rest of the colleague's tree (their own VAM firmware, PKI tooling,
station-link Python tools, the V2X2MAP bridge) stays out of this repository
and gitignored; nothing is pushed to their repository. NOTES.md, docs/06,
TODO.md and the pcap verifier's usage line point at the new location.

obu-firmware/external/vanetza-idf/vanetza/security/sha.cpp

@@ -0,0 +1,49 @@
+#include <vanetza/security/sha.hpp>
+#ifdef VANETZA_WITH_CRYPTOPP
+#include <cryptopp/sha.h>
+#endif
+#ifdef VANETZA_WITH_OPENSSL
+#include <openssl/sha.h>
+#endif
+
+namespace vanetza
+{
+namespace security
+{
+
+Sha256Digest calculate_sha256_digest(const uint8_t* data, std::size_t len)
+{
+    Sha256Digest digest;
+#if defined VANETZA_WITH_OPENSSL
+    static_assert(SHA256_DIGEST_LENGTH == digest.size(), "size of OpenSSL SHA256_DIGEST_LENGTH does not match");
+    SHA256_CTX ctx;
+    SHA256_Init(&ctx);
+    SHA256_Update(&ctx, data, len);
+    SHA256_Final(digest.data(), &ctx);
+#elif defined VANETZA_WITH_CRYPTOPP
+    static_assert(CryptoPP::SHA256::DIGESTSIZE == digest.size(), "size of CryptoPP::SHA256 does not match digest");
+    CryptoPP::SHA256 hash;
+    hash.CalculateDigest(digest.data(), data, len);
+#else
+#   error "no SHA256 implementation available"
+#endif
+    return digest;
+}
+
+Sha384Digest calculate_sha384_digest(const uint8_t* data, std::size_t len)
+{
+    Sha384Digest digest;
+#if defined VANETZA_WITH_OPENSSL
+    SHA384(data, len, digest.data());
+#elif defined VANETZA_WITH_CRYPTOPP
+    static_assert(CryptoPP::SHA384::DIGESTSIZE == digest.size(), "size of CryptoPP::SHA384 does not match digest");
+    CryptoPP::SHA384 hash;
+    hash.CalculateDigest(digest.data(), data, len);
+#else
+#   error "no SHA384 implementation available"
+#endif
+    return digest;
+}
+
+} // namespace security
+} // namespace vanetza