Keep the colleague's microbu-esp32c5 tree in this repository

obu-firmware builds against vanetza-idf from microbu-esp32c5/external, but
that tree was gitignored, so a clone of this repository could not build the
firmware it ships. It is now committed here as ordinary files in its own
folder, microbu-esp32c5/: the colleague's commit cf4b99f plus the V2X2MAP
bridge's signature verification (--trust) used on the bench. Nothing is
fetched from or pushed to the colleague's repository; this repository and
its remotes carry everything. The folder's own .gitignore keeps build output,
downloaded components and private key material out, as it did there; the
committed file set is identical to that repository's tracked files.

The ESP32-C5 is still flashed from obu-firmware/, which only takes
vanetza-idf from microbu-esp32c5/, so the two stay separate folders.
FLASHING.md says how to take a newer version of the colleague's tree (copy
it over the folder, rebuild, test, commit).

microbu-esp32c5/external/vanetza-idf/vanetza/security/v3/distance.hpp

@@ -0,0 +1,44 @@
+#pragma once
+#include <vanetza/security/v3/asn1_types.hpp>
+#include <vanetza/units/angle.hpp>
+#include <vanetza/units/length.hpp>
+
+namespace vanetza
+{
+
+// forward declaration
+struct PositionFix;
+
+namespace security
+{
+namespace v3
+{
+
+/**
+ * Calculate distance between two positions using Haversine formula
+ * 
+ * \param one a local position fix
+ * \param other a received location
+ * \return distance in meters
+ */
+units::Length distance(const PositionFix& one, const asn1::TwoDLocation& other);
+
+/**
+ * Convert ASN.1 latitude to GeoAngle
+ * 
+ * \param in ASN.1 security latitude
+ * \return GeoAngle
+ */
+units::GeoAngle convert_latitude(const asn1::Latitude& in);
+
+/**
+ * Convert ASN.1 longitude to GeoAngle
+ * 
+ * \param in ASN.1 security longitude
+ * \return GeoAngle
+ */
+units::GeoAngle convert_longitude(const asn1::Longitude& in);
+
+} // namespace v3
+} // namespace security
+} // namespace vanetza