Fix ArrowDeviceArray interface to pass address of event

[zeroshade]

Description

the sync_event member of ArrowDeviceArray needs to be a pointer to a cudaEvent_t, currently we're returning the cudaEvent_t directly. We need to be passing the address of the event. Thankfully this is a single line change, plus adding a test to confirm.

Checklist

• [x] I am familiar with the Contributing Guidelines.
• [x] New or existing tests cover these changes.
• [x] The documentation is up to date with these changes.

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[zeroshade]

CC @vyasr

[davidwendt]

/ok to test

[zeroshade]

Added calls to cudaEventSynchronize

[vyasr]

/ok to test

[zeroshade]

@vyasr anything else needed for this to get merged?

[davidwendt]

/merge