Use buffer in memory instead of file handle for decoder

[Denneisk]

AdvDupe2 uses a temporary file to store and process the dupe contents as a stream. This works, but adds unnecessary complexity by having to create a file on the actual file system, and can cause problems if there's an issue accessing that file.

Implementing the buffer using Lua might also improve speed.

[thegrb93]

I think I already tested it with SF stringstream and the performance was about the same. Was many years ago tho so not sure.