Improve module import time

[rpadmanabhan]

Is your feature request related to a problem? Please describe. It takes almost 4 seconds for muon to import, it would be nice if we could import muon < 1s like scanpy

Python 3.9.12 (main, Apr  5 2022, 06:56:58) 
[GCC 7.5.0] :: Anaconda, Inc. on linux
Type "help", "copyright", "credits" or "license" for more information.
>>> import timeit
>>> import_time = timeit.timeit("import muon", number=1)
>>> print("Time taken to import muon:", import_time, "seconds")
Time taken to import muon: 4.092318220064044 seconds

Describe the solution you'd like I have not dug into the code too much, maybe delaying any costly setups/internal imports to later when needed so most users can avoid the initial delay.

Describe alternatives you've considered N/A

Additional context N/A