This does introduce some not-so-nice things, like having to annotate each
`__init__` function with `-> None`. However, the benefits of having static
type checking in a complex bit of software like BAT outweigh the downsides.
- Tracer now iterates over blocks in disk order.
- Packer copies files per directory, in a separate thread.
- Packer only copies files if they don't exist yet.
- Packer also copies file permissions.
No path rewriting yet, just simply copying the dependencies. They are
copied to the target directory + the path relative to the current working
directory. For example:
bat pack scenes/05-barber/05_02_C-agent_focused/05_02_C.lighting.blend /tmp/packer
will write to
/tmp/packer/scenes/05-barber/05_02_C-agent_focused/05_02_C.lighting.blend
and will copy ./path/to/file → /tmp/packer/path/to/file
