Re-work some NBT handling for better performance, and handle big files

This commit includes some default NBT formatting settings which result
in smaller files, and re-implements NbtVirtualFile to be a
LightVirtualFile. Part of that re-implementation is to make NBT files
only write to disk when saved manually, which is the behavior I
originally wanted anyways. This feels much safer and more stable than
whatever was happening originally.

By being a LightVirtualFile it seems the size limits / requirements on
Psi files are relaxed, but I don't fully understand the details. It
seems to handle larger NBT files better now.

Relevant issues: #1894 , #1893