Use max(uint64) for OOV lexeme rank

[adrianeboyd]

Description

Use max(uint64) for OOV lexeme rank

Types of change

Bug fix.

Checklist

• I have submitted the spaCy Contributor Agreement.
• I ran the tests, and all new and existing tests passed.
• My changes don't require a change to the documentation, or if they do, I've added all required information.

[adrianeboyd]

The tests will fail because the version of thinc isn't available.

Is there a better way to define OOV_RANK in a way that's fast in Lexeme and elsewhere?

I also couldn't think of a good way to write tests for this?

[honnibal]

I think we can do:

from libc.stdint cimport UINT64_MAX

OOV_RANK = UINT64_MAX

In the test, I think we can test whether OOV_RANK is 2**64-1`? That's what it should be, in theory, and we probably want to know about it if it's not.

[adrianeboyd]

util isn't a great place to put it but nothing else seemed better and I was trying not to call a function if possible. If you want to call a function in the python parts, I think you may as well use numpy.iinfo(numpy.uint64).max. How about this version with no local math?

[honnibal]

Okay, looks good!