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FLASHING.md says how to take a newer version of the colleague's tree (copy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/common/tests/byte_view.cpp

@@ -0,0 +1,28 @@
+#include <gtest/gtest.h>
+#include <vanetza/common/byte_view.hpp>
+#include <vanetza/common/byte_buffer_convertible.hpp>
+
+using namespace vanetza;
+
+TEST(ByteView, range_buffer) {
+    ByteBuffer buffer = {1, 2, 3, 4, 5, 6, 7, 8};
+    byte_view_range view = create_byte_view(buffer);
+    ASSERT_EQ(buffer.size(), view.size());
+    EXPECT_EQ(1, *view.begin());
+    EXPECT_EQ(3, view[2]);
+}
+
+TEST(ByteView, range_convertible) {
+    byte_view_range view = create_byte_view(ByteBuffer());
+    {
+        std::string buffer = "temporary data";
+        ByteBufferConvertible convertible { std::move(buffer) };
+        // view should now own a byte buffer copy of original string
+        view = create_byte_view(convertible);
+    }
+
+    ASSERT_EQ(14, view.size());
+    EXPECT_EQ('t', view[0]);
+    EXPECT_EQ('y', view[8]);
+    EXPECT_EQ('d', view[10]);
+}