Logging and mask updates, resize speedup

[slimbuck]

This PR:

• updates logging so the script can log its invocations to stdout without the invoked functions spamming stdout.
• change mask handling to be a bit more robust
• speedup resize by a factor of 2 by using imagemagick more effectively (this change was submitted upstream too Resize 2x speedup graphdeco-inria/gaussian-splatting#680).

[yak32]

is this less than 256?

[slimbuck]

Yep. The problem before was actually os.system which returns a 16-bit number on unix "whose low byte is the signal number that killed the process, and whose high byte is the exit status". This was causing the strange numbers.

subprocess.check_call doesn't do this, but supplies returncode directly in the exception.