This adds the ability to "retag" a universal2 fused wheel. When running
delocate-fuse with this flag, it will update the filename and the
dist-info file of the fused wheel to reflect that it is a universal2
wheel.

This updates '_get_archs_and_version_from_wheel_name' to check if both
arm64 and x86_64 platform tags are in the wheel's filename. If they are
both present, it changes the returned arch to be universal2 with the
appropriate version.

This is now much simpler and more generalized. It first updates the name
to contain platform tags from both from_wheel and to_wheel. Next it
calls '_check_and_update_wheel_name' which fixes any issues with the
name AND will convert it to universal2 if necessary. And finally, it
calls '_update_wheelfile' to update the info in the WHEEL file to match
the new name.

This also updates the fuse function to support pathlib paths and updates
the retagging function to use pathlib paths.

This also required some typing changes to functions called by
fused_trees.

Depending on the version of each wheel being fused, the universal2
wheel's version can be either the x86_64 or the arm64 wheel's version.
The first test for this is testing the scenario where the x86_64 wheel's
version should be used. This new test is tesing the scenario where the
arm64 wheel's version should be used.

This moves the old 'delocate-fuse' functionality into the new
'delocate-merge' command. Running 'delocate-fuse' will now print a
message notifying the user of this change and then exit with an exit
code of 1. This also updates relevant tests, the changelog, and the
README.