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/common/confident_quantity.hpp

@@ -0,0 +1,77 @@
+#ifndef CONFIDENT_QUANTITY_HPP_B2XVJERI
+#define CONFIDENT_QUANTITY_HPP_B2XVJERI
+
+#include <limits>
+
+namespace vanetza
+{
+
+/**
+ * ConfidentQuantity combines a boost::quantity value with a confidence level.
+ *
+ * Usually, a confidence level of 95% is used in ITS specifications.
+ * If no confidence level is explicitly given a worst case value is used, i.e.
+ * the maximum value representable by the underlying type or infinity.
+ */
+template<typename T>
+class ConfidentQuantity
+{
+public:
+    constexpr T worst_confidence() const
+    {
+        using value_type = typename T::value_type;
+        return T::from_value(std::numeric_limits<value_type>::has_infinity ?
+            std::numeric_limits<value_type>::infinity() :
+            std::numeric_limits<value_type>::max());
+    }
+
+    constexpr T default_value() const
+    {
+        using value_type = typename T::value_type;
+        return T::from_value(std::numeric_limits<value_type>::has_quiet_NaN ?
+            std::numeric_limits<value_type>::quiet_NaN() : value_type());
+    }
+
+    constexpr bool is_nan(const T& t) const
+    {
+        return t.value() != t.value();
+    }
+
+    ConfidentQuantity() :
+        m_value(default_value()), m_confidence(worst_confidence()) {}
+    ConfidentQuantity(const T& value) :
+        m_value(value), m_confidence(worst_confidence()) {}
+    ConfidentQuantity(const T& value, const T& confidence) :
+        m_value(value), m_confidence(!is_nan(confidence) ? confidence : worst_confidence()) {}
+
+    ConfidentQuantity(const ConfidentQuantity&) = default;
+    ConfidentQuantity& operator=(const ConfidentQuantity&) = default;
+    ConfidentQuantity(ConfidentQuantity&&) = default;
+    ConfidentQuantity& operator=(ConfidentQuantity&&) = default;
+
+    void assign(const T& value, const T& confidence)
+    {
+        m_value = value;
+        m_confidence = !is_nan(confidence) ? confidence : worst_confidence();
+    }
+
+    const T& value() const
+    {
+        return m_value;
+    }
+
+    const T& confidence() const
+    {
+        return m_confidence;
+    }
+
+private:
+    T m_value;
+    T m_confidence;
+};
+
+
+} // namespace vanetza
+
+#endif /* CONFIDENT_QUANTITY_HPP_B2XVJERI */
+