Interface impedance between NMR API and Windows EX_RUNDOWN_REF APIs

The NMR APIs are designed to be completely asynchronous, with detach operations returning pending if the provider data is in use.
The Windows EX_RUNDOWN_REF are synchronous, with rundown blocking until completion.

The NMR API contract requires some form of rundown protection to prevent use after detach, but the only Windows API are synchronous ones.

Proposal:
Replace EX_RUNDOWN_REF with an asynchronous contract.

Start by reviewing the NMR asynchronous detach contract and the Windows EX_RUNDOWN_REF behavior described in the issue. Determine an asynchronous rundown design that prevents use after detach; done means the synchronous dependency is replaced by an agreed, implemented contract with corresponding validation.

Written by the indexing model from the issue text.