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.
For regular file transfers (so to a directory, not to a ZIP file or S3
storage), use multi-threaded transfer when compressing. Compressing is
CPU-bound, so using multiple threads speeds things up considerably
(packing a Spring lighting file went from 6min30 single-threaded to
2min13 multi-threaded on my machine).
The .get() function raises a queue.Empty exception anyway, so there was
no real need for the .empty() call. Furthermore, it turned out to really
slow things down.
For this to work well I also had to remove the sorting of blocks in
trace.deps(). The sorting caused the first `yield` to be executed only
after each blend file was opened, which means that the consuming for-loop
takes a long time to hit its first iteration. As a result, it would respond
slowly to abort requests. By not sorting the first `yield` is much sooner,
resolving this issue.
Both the dependency Tracer class and the Packer class now support a
callback object, where the latter is a subclass of the former.
For file transfers running in a separate thread, there is a thread-safe
wrapper for progress callbacks. This wrapper can be called from any thread,
and calls the wrapped callback object from the main thread. This way the
callback implementation itself doesn't have to worry about threading
issues.
Function declarations that have no type annotations at all will be skipped
by mypy. Adding an explicit `-> None` tells mypy to run on those functions
too.
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.
