Add basic cunumeric.patch module

[bryevdv]

This PR adds a very basic cunumeric.patch module that can be imported early in a script to "automatically" replace NumPy with cuNumeric. With the following example script:

import cunumeric.patch

import numpy as np

a = np.random.randn(4, 5)

np.argmin(a, axis=0)
np.argmin(a, axis=1)

np.argmax(a, axis=0)
np.argmax(a, axis=1)

The desired coverage results are generated:

~/work/cunumeric branch-22.03*
legate37 ❯ legate /tmp/foo.py  -cunumeric:report:coverage 
cuNumeric API coverage: 5/5 (100.0%)

Notes

• This is not yet quite "zero-change", but is a necessary start, and can be utilized immediately, with one line of code added. Assuming a -m option is implemented in legion in the future, the it should become possible to update cunumeric patch with a "main" that affords this usage via the command line:

  legate -m cunumeric.patch foo.py
  

  without making any source changes at all.

• True "zero-change" would require changes to legate but there would be questions to answer about having to make legate know about cunumeric.

• The patching is very simple-minded, and may have edge-cases or shortcomings. E.g. I had hoped to be able to warn loudly in case numpy was already imported, but cunumeric itself imports numpy, so that is not feasible. We cannot rely on the presence or absence of numpy in sys.modules to condition a warning. I would recommend not widely promoting this module, and keeping it intended as a tool for experienced dev-rel for this reason.

[magnatelee]

LGTM. Feel free to merge this. (I believe the failures have nothing to do with this PR.)