windows: resizable nostrdb, 16gb issue

[jb55]

Right now we set a 16GB nostrdb mapsize on windows. Unfortunately do to the way lmdb works on windows, it allocates a file that is 16GB in size instead of creating a virtual memory map that expands in size.

Monero solved this somehow so we should look at how they do it. I think it involves resizing the database occasionally when it gets close to the limit.