Includes various enhancements/fixes discovered as testing:

• Implement Python storage == operator.
• Fix incorrect logical sense of the buffer read-only flag.
• Add a str method to device_array which only prints the contents (not all of the other array info).
• Captures any exception raised by the main coroutine and marshals it to the caller (was printing in an unhandled exception handler and then dropping on the floor).
• Adds an exception translator for IREE status exceptions, which maps certain status codes to more appropriate Python exception classes.
• Adds size validation to device_array construct from storage constructor.

These are fairly complete unit level tests of all array functionality, including some scheduling (since the tests await for device idle, which requires that all of the buffer timeline tracking is done properly).