fix(payload): switch raw payload metadata fields from u32 to u64

Payload_img_design.md

@@ -43,10 +43,10 @@ The flow is:
 ### Format
 
 - Magic: `LBPAYLD1` (8 bytes)
-- Then: little-endian `u32` file count
+- Then: little-endian `u64` file count
 - Repeated entries:
-  - little-endian `u32` name length
-  - little-endian `u32` file size
+  - little-endian `u64` name length
+  - little-endian `u64` file size
   - file name bytes (no terminator)
   - file bytes
 
@@ -69,21 +69,21 @@ set -e
 out="${1:-external.img}"
 list="${2:-external.list}"
 
-write_u32le() {
+write_u64le() {
   v="$1"
-  printf '%08x' "$v" | sed -E 's/(..)(..)(..)(..)/\4\3\2\1/' | xxd -r -p
+  printf '%016x' "$v" | sed -E 's/(..)(..)(..)(..)(..)(..)(..)(..)/\8\7\6\5\4\3\2\1/' | xxd -r -p
 }
 
 count="$(wc -l < "${list}" | tr -d ' ')"
 : > "${out}"
 printf 'LBPAYLD1' >> "${out}"
-write_u32le "${count}" >> "${out}"
+write_u64le "${count}" >> "${out}"
 
 while read -r name path; do
   [ -n "${name}" ] || continue
   size="$(wc -c < "${path}" | tr -d ' ')"
-  write_u32le "${#name}" >> "${out}"
-  write_u32le "${size}" >> "${out}"
+  write_u64le "${#name}" >> "${out}"
+  write_u64le "${size}" >> "${out}"
   printf '%s' "${name}" >> "${out}"
   cat "${path}" >> "${out}"
 done < "${list}"