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/remove_prefix_from_filename.cmake

@@ -0,0 +1,15 @@
+if(NOT DEFINED ASN1C_OUTPUT_DIR)
+    message(FATAL_ERROR "Missing ASN.1 output directory (ASN1C_OUTPUT_DIR)")
+elseif(NOT DEFINED ASN1C_PREFIX)
+    message(FATAL_ERROR "Missing ASN.1 prefix (ASN1C_PREFIX)")
+endif()
+
+message(STATUS "removing prefix '${ASN1C_PREFIX}' from files in ${ASN1C_OUTPUT_DIR}")
+file(GLOB _files ${ASN1C_OUTPUT_DIR}/${ASN1C_PREFIX}*)
+foreach(_from ${_files})
+    get_filename_component(_dir ${_from} DIRECTORY)
+    get_filename_component(_name ${_from} NAME)
+    string(REPLACE "${ASN1C_PREFIX}" "" _to "${_name}")
+    file(RENAME ${_from} ${_dir}/${_to})
+endforeach()
+