Convert target path from Path to str & PurePath

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.

blender_asset_tracer/pack/zipped.py

@@ -37,7 +37,8 @@ class ZipPacker(Packer):
     """Creates a zipped BAT Pack instead of a directory."""
 
     def _create_file_transferer(self) -> transfer.FileTransferer:
-        return ZipTransferrer(self.target.absolute())
+        target_path = pathlib.Path(self._target_path)
+        return ZipTransferrer(target_path.absolute())
 
 
 class ZipTransferrer(transfer.FileTransferer):
@@ -61,7 +62,7 @@ class ZipTransferrer(transfer.FileTransferer):
             for src, dst, act in self.iter_queue():
                 assert src.is_absolute(), 'expecting only absolute paths, not %r' % src
 
-                dst = dst.absolute()
+                dst = pathlib.Path(dst).absolute()
                 try:
                     relpath = dst.relative_to(zippath)