query: also teard down on ctx done

[MichaelMure]

I'm not entirely sure this should be supported but at the moment you could expect to terminate a query:

• call Close() on the Result
• cancel the context

The second one though doesn't work as cancelling the context doesn't kill the query. This PR address that problem.

[guseggert]

Have you gone through where this is (potentially) used to make sure that returning context.Canceled or context.DeadlineExceeded are handled gracefully/correctly upstream? Would it make sense to just swallow ctx.Err() and return nothing? (which is what happens when results.Close() is called, also what happens on processctx.WithContext(ctx))

[MichaelMure]

My thinking is that calling results.Close() is a voluntary action from the caller side.

On the other hand, killing a query with the context is typically done higher in the call stack, with a timeout or linked to a request lifecycle. There, the caller side might not know and an error would help distinguish a success or failure termination.

[guseggert]

I did some spot checking of how these bubble up into go-ipfs and it looks okay to me. Thanks!