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/signature.cpp

@@ -0,0 +1,72 @@
+#ifndef FA909143_0CE7_4397_A42B_5CDA56AB4716
+#define FA909143_0CE7_4397_A42B_5CDA56AB4716
+
+#include <vanetza/security/ecc_point.hpp>
+#include <vanetza/security/signature.hpp>
+#include <cassert>
+
+namespace vanetza
+{
+namespace security
+{
+
+EcdsaSignatureFuture::EcdsaSignatureFuture(std::shared_future<EcdsaSignature> future,
+        EcdsaSignature placeholder) :
+    m_future(future), m_placeholder(std::move(placeholder))
+{
+    if (!m_future.valid()) {
+        throw std::invalid_argument("EcdsaSignature future has to be valid");
+    }
+}
+
+const EcdsaSignature& EcdsaSignatureFuture::get() const
+{
+    assert(m_future.valid());
+    const EcdsaSignature& signature = m_future.get();
+    assert(signature.s.size() == m_placeholder.s.size());
+    assert(signature.R.which() == m_placeholder.R.which());
+    assert(get_length(signature.R) == get_length(m_placeholder.R));
+    return signature;
+}
+
+std::size_t EcdsaSignatureFuture::size() const
+{
+    return get_length(m_placeholder.R) + m_placeholder.s.size();
+}
+
+ByteBuffer extract_signature_buffer(const SomeEcdsaSignature& sig)
+{
+    struct extraction_visitor : public boost::static_visitor<>
+    {
+        void operator()(const EcdsaSignature& sig)
+        {
+            m_buffer = convert_for_signing(sig.R);
+            m_buffer.insert(m_buffer.end(), sig.s.begin(), sig.s.end());
+        }
+
+        void operator()(const EcdsaSignatureFuture& sig_future)
+        {
+            const EcdsaSignature& sig = sig_future.get();
+            (*this)(sig);
+        }
+
+        ByteBuffer m_buffer;
+    };
+
+    extraction_visitor visitor;
+    boost::apply_visitor(visitor, sig);
+
+    return visitor.m_buffer;
+}
+
+ByteBuffer extract_signature_buffer(const Signature& sig)
+{
+    ByteBuffer buffer = sig.r;
+    buffer.insert(buffer.end(), sig.s.begin(), sig.s.end());
+    return buffer;
+}
+
+} // namespace security
+} // namespace vanetza
+
+#endif /* FA909143_0CE7_4397_A42B_5CDA56AB4716 */