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FLASHING.md says how to take a newer version of the colleague's tree (copy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/asn1/support/asn_internal.c

@@ -0,0 +1,50 @@
+#include "asn_internal.h"
+
+ssize_t
+asn__format_to_callback(int (*cb)(const void *, size_t, void *key), void *key,
+                        const char *fmt, ...) {
+    char scratch[64];
+    char *buf = scratch;
+    size_t buf_size = sizeof(scratch);
+    int wrote;
+    int cb_ret;
+
+    do {
+        va_list args;
+        va_start(args, fmt);
+
+        wrote = vsnprintf(buf, buf_size, fmt, args);
+        va_end(args);
+        if(wrote < (ssize_t)buf_size) {
+            if(wrote < 0) {
+                if(buf != scratch) FREEMEM(buf);
+                return -1;
+            }
+            break;
+        }
+
+        buf_size <<= 1;
+        if(buf == scratch) {
+            buf = MALLOC(buf_size);
+            if(!buf) {
+              return -1;
+            }
+        } else {
+            void *p = REALLOC(buf, buf_size);
+            if(!p) {
+                FREEMEM(buf);
+                return -1;
+            }
+            buf = p;
+        }
+    } while(1);
+
+    cb_ret = cb(buf, wrote, key);
+    if(buf != scratch) FREEMEM(buf);
+    if(cb_ret < 0) {
+        return -1;
+    }
+
+    return wrote;
+}
+