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/unit_interval.hpp

@@ -0,0 +1,96 @@
+#ifndef UNIT_INTERVAL_HPP_BG1EK7QX
+#define UNIT_INTERVAL_HPP_BG1EK7QX
+
+#include <boost/operators.hpp>
+#include <iterator>
+#include <type_traits>
+
+namespace vanetza
+{
+
+/**
+ * UnitInterval represents a number within the unit interval [0.0, 1.0]
+ *
+ * UnitInterval is not an interval on its own but limits all numbers to this interval.
+ * Mantissa (positive fractional part of a real number) behaves differently, thus:
+ * - Mantissa(42.1234) = 0.1234
+ * - UnitInterval(42.1234) = 1.0
+ * UnitInterval is also related to "(proper) decimal fraction" but latter does not include 1.0.
+ */
+class UnitInterval :
+    boost::arithmetic<UnitInterval>,
+    boost::arithmetic<UnitInterval, double>,
+    boost::totally_ordered<UnitInterval>
+{
+public:
+    constexpr UnitInterval() : UnitInterval(0.0) {}
+    constexpr explicit UnitInterval(double v) : m_value(clamp(v)) {}
+    UnitInterval(const UnitInterval&) = default;
+    UnitInterval& operator=(const UnitInterval&) = default;
+
+    // arithmetic
+    UnitInterval& operator+=(const UnitInterval&);
+    UnitInterval& operator-=(const UnitInterval&);
+    UnitInterval& operator*=(const UnitInterval&);
+    UnitInterval& operator/=(const UnitInterval&);
+
+    UnitInterval& operator+=(double);
+    UnitInterval& operator-=(double);
+    UnitInterval& operator*=(double);
+    UnitInterval& operator/=(double);
+
+    // partially ordered
+    bool operator<(const UnitInterval& other) const;
+    bool operator==(const UnitInterval& other) const;
+
+    double value() const { return m_value; }
+    UnitInterval complement() const;
+
+private:
+    constexpr static double clamp(double v)
+    {
+        return (v > 1.0 ? 1.0 : (v < 0.0 ? 0.0 : v));
+    }
+    UnitInterval& clamp();
+
+    double m_value;
+};
+
+/**
+ * Calculate mean value of two unit intervals
+ * \param lhs
+ * \param rhs
+ * \return mean unit interval
+ */
+UnitInterval mean(UnitInterval lhs, UnitInterval rhs);
+
+/**
+ * Calculate mean of a range of unit intervals
+ * \param begin of range
+ * \params end of range
+ * \reutrn mean unit interval
+ */
+template<
+    typename Iterator,
+    typename std::enable_if<
+        std::is_convertible<typename std::iterator_traits<Iterator>::value_type, UnitInterval>::value,
+        int>::type = 0
+>
+UnitInterval mean(Iterator begin, Iterator end)
+{
+    unsigned count = 0;
+    double accu = 0.0;
+
+    for (Iterator it = begin; it != end; ++it)
+    {
+        accu += it->value();
+        ++count;
+    }
+
+    return UnitInterval { count > 1 ? (accu / count) : accu };
+}
+
+} // namespace vanetza
+
+#endif /* UNIT_INTERVAL_HPP_BG1EK7QX */
+