FileAttributes ModTime int32

[GM64]

Hi,

I have a problem when accessing modification time of remote files over sftp.
the remote file has an mod-time of Dec 12, 2049. For mod-times greater than maxInt32 (some date in 2038) i get a negative time.
the problem is in the class net.schmizz.sshj.sftp.FileAttributes. The the mod-time is set as int32

[exceptionfactory]

The modification time defined as an int32 aligns with SFTP Protocol Version 3. The SFTP Protocol Version 4 specification changes the type to 64 bits. There are some conditional checks for the SFTP protocol version, so building on that approach could provide a solution.