How does macOS store Unix file permissions in ZIP files
The permissions are stored in the same manner as they are on other Unixoid systems, such as for example Linux.

If you look at the central directory header in the zip-file, you have for each file stored in the Zip-file a field called "external file attributes". The field is at byte 36 in the header and is 4 bytes long.

The two last bytes in that field contains the file permissions on macOS - to be precise it is the last 9 bits (the least significant 9 bits). Their meaning is just like traditional Unix file permissions.