The target path is just read as string from the CLI now, to allow more
complex targets (such as URLs) that don't directly map to a path.
The Packer subclass now handles the conversion from that string to a
`pathlib.PurePath`, and specific subclasses & transfer classes can convert
those to a `pathlib.Path` to perform actual filesystem operations when
necessary.
This makes BAT skip assets that are referred to with an absolute path.
It is assumed that the receiver of the BAT pack can access those assets
at the same path.
This will cause a nice speedup if the temporary directory happens to be on
the same file system as the target directory for the BAT Pack. This can be
influenced by setting an environment variable; see the documentation for
[tempfile.gettempdir](https://docs.python.org/3/library/tempfile.html#tempfile.gettempdir)
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
