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/v2/sign_service.hpp

@@ -0,0 +1,75 @@
+#ifndef AD03EF9D_246E_48D3_83F0_9983ADF0C454
+#define AD03EF9D_246E_48D3_83F0_9983ADF0C454
+
+#include <vanetza/security/sign_service.hpp>
+#include <vanetza/security/v2/certificate_provider.hpp>
+#include <vanetza/security/v2/secured_message.hpp>
+#include <vanetza/security/v2/sign_header_policy.hpp>
+
+namespace vanetza
+{
+namespace security
+{
+
+// forward declarations
+class Backend;
+
+namespace v2
+{
+
+// forward declarations
+class CertificateProvider;
+
+/**
+ * SignService immediately signing the message using given
+ */
+class StraightSignService : public SignService
+{
+public:
+   StraightSignService(CertificateProvider&, Backend&, SignHeaderPolicy&);
+   SignConfirm sign(SignRequest&&) override;
+
+private:
+    CertificateProvider& m_certificates;
+    Backend& m_backend;
+    SignHeaderPolicy& m_policy;
+};
+
+/**
+ * SignService deferring actually signature calculation using EcdsaSignatureFuture
+ */
+class DeferredSignService : public SignService
+{
+public:
+    DeferredSignService(CertificateProvider&, Backend&, SignHeaderPolicy&);
+    SignConfirm sign(SignRequest&&) override;
+
+private:
+    CertificateProvider& m_certificates;
+    Backend& m_backend;
+    SignHeaderPolicy& m_policy;
+};
+
+/**
+ * SignService without real cryptography but dummy signature
+ */
+class DummySignService : public SignService
+{
+public:
+    /**
+     * \param rt runtime for appropriate generation time
+     * \param si signer info attached to header fields of secured message
+     */ 
+    DummySignService(const Runtime& rt, const SignerInfo& si);
+    SignConfirm sign(SignRequest&&) override;
+
+private:
+    const Runtime& m_runtime;
+    SignerInfo m_signer_info;
+};
+
+} // namespace v2
+} // namespace security
+} // namespace vanetza
+
+#endif /* AD03EF9D_246E_48D3_83F0_9983ADF0C454 */