Fixes for bugs found during manual use

(1) In _ingestion, it's the "details" attribute of a
NoSuchMethodException that we want. The "message" is inherited from the
base Exception class.

(2) In _transmission, use a proper sum type for representing operation
abortion. Trying to overload the existing _completion value for
status-and-details-when-aborting was trying to be too clever.

(3) In _calls... oof. Just look. Oof. Test coverage for this code path
is added.

(4) In _service, the application-provided
face.MultiMethodImplementation isn't directly callable, but rather
exposes a method named "service".

(5) In crust.implementations, the wrapping that we've put around the
application-provided face.MultiMethodImplementation *is* directly
callable, and *does not* expose a method named "service".

(6) Also in crust.implementations, base.NoSuchMethodError's constructor
takes a code value and a details value.

(7) Again in crust.implementations, the application-provided
face.MultiMethodImplementation may be None, and if it is None, we
shouldn't wrap it with an adaptation function that would only raise a
TypeError at a later time.