feat: context everywhere and non-blocking results about goupnp HOT 2 OPEN

Turns out I used an older version of the library. Context does indeed exist in the SSDP search API, although it doesn't appear to be respected in the httpu client, which still runs for its full duration even if the context is canceled. I added the following to the Do method:

	ctx, cancel := context.WithTimeout(req.Context(), timeout)
	defer cancel()
	go func() {
		<-ctx.Done()
		httpu.conn.SetDeadline(time.Now())
	}()

This terminated the httpu call on time, which is I believe the way context is supposed to work. Would something like that be considered a bug fix?

As for shortening the search period: I thought we could use timeout contexts for searches, but this won't work: afaik there are more calls after to get the "device info" (don't know the details of upnp - apologies). If we cancel the context to stop the search, we can't make those requests. For that, we still need to either (a) stream the results as they come available or (b) keep using a timeout (but perhaps we can make it more granular?). Context can still be used as a last resort to terminate everything quickly on teardown.

I also tried measuring the results on my Netgear home router, and it was very fast (1-3ms). Even if the SSDP protocol requires MX >= 1, I'd really want to act on those early results, especially if that's the common case.

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This seems like a good request. We'd need to retain the existing API for any code using it, perhaps:

1. Adding a DoWithContext method that otherwise acts like Do, but provides a way to pass back results as they come in, and respects the context completion.
2. And then Implement Do in terms of DoWithContext so that there's only one implementation.

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