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/bit_number.hpp

@@ -0,0 +1,44 @@
+#ifndef BIT_NUMBER_HPP_H3ODBQR7
+#define BIT_NUMBER_HPP_H3ODBQR7
+
+#include <boost/operators.hpp>
+#include <cstddef>
+#include <type_traits>
+
+namespace vanetza {
+
+/**
+ * BitNumber restricts the value range by the given width
+ *
+ * \tparam T underlying integral type
+ * \tparam WIDTH number of bits used to represent a number
+ */
+template<typename T, std::size_t WIDTH>
+class BitNumber : public boost::totally_ordered<BitNumber<T, WIDTH>>
+{
+    static_assert(std::is_integral<T>::value == true,
+            "only integral types are supported");
+    static_assert(sizeof(T) * 8 > WIDTH,
+            "width has to be less than size of underlying type");
+
+public:
+    static constexpr T mask = (1 << WIDTH) - 1; /**< excessive bits are masked */
+    static constexpr std::size_t bits = WIDTH; /**< number of bits used */
+    typedef T value_type; /**< underlying (integral) value type */
+
+    BitNumber() : mValue(0) {}
+    BitNumber(T value) : mValue(value & mask) {}
+    BitNumber& operator=(T value) { mValue = value & mask; return *this; }
+    T raw() const { return mValue; }
+
+    bool operator<(BitNumber other) const { return mValue < other.mValue; }
+    bool operator==(BitNumber other) const { return mValue == other.mValue; }
+
+private:
+    T mValue;
+};
+
+} // namespace vanetza
+
+#endif /* BIT_NUMBER_HPP_H3ODBQR7 */
+