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FLASHING.md says how to take a newer version of the colleague's tree (copy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

@@ -0,0 +1,45 @@
+#include "pem.hpp"
+#include <gtest/gtest.h>
+
+using namespace vanetza::pki;
+
+static const std::string privKeyPem =
+    "-----BEGIN EC PRIVATE KEY-----\n"
+    "MHcCAQEEIHlpKyVDNCQ2x5IFeBelQyyvANI8iTFIoCTfNARm1LVxoAoGCCqGSM49\n"
+    "AwEHoUQDQgAEvfkk5CcwIqP29fGu9n6kXmojUpV2xUlnM2BwJMoYmiVU7lF9p7tu\n"
+    "+KUbGlhPaYLN0UZ13KQTmi3gV3aLolyXUw==\n"
+    "-----END EC PRIVATE KEY-----";
+
+static const vanetza::ByteBuffer privKeyRaw = {
+    0x79, 0x69, 0x2b, 0x25, 0x43, 0x34, 0x24, 0x36,
+    0xc7, 0x92, 0x05, 0x78, 0x17, 0xa5, 0x43, 0x2c,
+    0xaf, 0x00, 0xd2, 0x3c, 0x89, 0x31, 0x48, 0xa0,
+    0x24, 0xdf, 0x34, 0x04, 0x66, 0xd4, 0xb5, 0x71
+};
+
+TEST(ReadPemPrivateKey, valid_prime256v1)
+{
+    boost::optional<PrivateKey> key = parse_pem_private_key(privKeyPem);
+    ASSERT_TRUE(key);
+    EXPECT_EQ(KeyType::NistP256, key->type);
+    EXPECT_EQ(privKeyRaw, key->key);
+}
+
+TEST(ReadPemPrivateKey, invalid_pem)
+{
+    EXPECT_FALSE(parse_pem_private_key("not a PEM"));
+    EXPECT_FALSE(parse_pem_private_key(""));
+}
+
+TEST(WritePemPrivateKey, roundtrip_generated)
+{
+    for (KeyType type : { KeyType::NistP256, KeyType::BrainpoolP256r1, KeyType::BrainpoolP384r1 }) {
+        PrivateKey generated = generate_private_key(type);
+        std::string pem = make_pem(generated);
+
+        boost::optional<PrivateKey> parsed = parse_pem_private_key(pem);
+        ASSERT_TRUE(parsed);
+        EXPECT_EQ(generated.type, parsed->type);
+        EXPECT_EQ(generated.key, parsed->key);
+    }
+}