Fix _util.device_from_ctx

[ksimpson-work]

The obvious issue is that both of these call get_device_from_ctx which references the unimported Device(). Importing it would cause a circular dependency. Importing it within the get_device_from_ctx solves that issue. A couple other little issues in the method itself are also addressed.

Expected behaviour is: The tests added, should fail without each of the _utils changes. They should pass with the changes. This was observed locally.

Closes #202

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[ksimpson-work]

/ok to test

[leofang]

I am not sure I follow. self._device_id could be None if we wrap a foreign stream using Device.create_stream(obj=some_foreign_stream_object). Then, the cuStreamGetCtx -> (set to the stream ctx) ->cuCtxGetDevice -> (set back to original ctx) combo is the only way to reliably retrieve the device ID. get_device_from_ctx is meant to make this combo cleaner.

How did you encounter a circular dependency? It might be an overlook in our test coverage depending on what the trigger path is. It is true that we forgot to import Device in get_device_from_ctx (good catch!), but circular dependency can be easily resolved by importing the object inside the function, as is already done in Stream.device.

[ksimpson-work]

Thankyou for pointing out my oversight. I now clearly see that device_id is None when a foreign stream is provided. There are still some issues which I will seek to address, and will switch this from draft once I get it working / identify the problem.

[ksimpson-work]

The changes

import Device inside function to avoid circular import
handle -> _handle
compare int(ctx) based on:

cdef class CUcontext:
"""

A regular context handle

Methods
-------
getPtr()
    Get memory address of class instance

"""
def __cinit__(self, void_ptr init_value = 0, void_ptr _ptr = 0):
    if _ptr == 0:
        self._ptr = &self.__val
        self._ptr[0] = <cydriver.CUcontext>init_value
    else:
        self._ptr = <cydriver.CUcontext *>_ptr
def __init__(self, *args, **kwargs):
    pass
def __repr__(self):
    return '<CUcontext ' + str(hex(self.__int__())) + '>'
def __index__(self):
    return self.__int__()
def __int__(self):
    return <void_ptr>self._ptr[0]
def getPtr(self):
    return <void_ptr>self._ptr

[leofang]

LGTM, blocking the merge until we conclude beta 1 QA process.