fix(cpio): fixed checksum calculation to handle 4 byte overflows

Checksum stored in the header is always 4 bytes in length, so when we calculate
the checksum, we need to sure that we only consider the 4bytes part and ommit
the overflown part.

Author: martonilles

unblob/handlers/archive/cpio.py

@@ -368,8 +368,7 @@ def valid_checksum(self, header, start_offset: int) -> bool:
 
         for chunk in iterate_file(self.file, start_offset, file_size):
             calculated_checksum += sum(bytearray(chunk))
-
-        return header_checksum == calculated_checksum
+        return header_checksum == calculated_checksum & 0xFF_FF_FF_FF
 
 
 class _CPIOExtractorBase(Extractor):