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/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;
+}
+