feat(ai): Enhance orchestrator selection by incorporating latency (livepeer#3043)

This commit introduces latency consideration into the orchestrator
selection process, addressing two key issues. Firstly, it resolves a
minor bug where the algorithm consistently selected known orchestrators
due to a condition that never evaluated to true (see [this
condition](https://github.com/livepeer/go-livepeer/blob/1239b4e56133003fe6a98a863cce6bdd6b5f2532/server/selection.go#L110)).
Secondly, this change ensures that, once all orchestrators have been
evaluated, the one with the fastest response time for a specific job is
chosen. While the current method for calculating latency is somewhat
basic, it sets the foundation for more sophisticated enhancements in the
future.

Co-authored-by: Brad P <0xb79orch@gmail.com>

Author: rickstaa

server/ai_process.go

@@ -93,7 +93,9 @@ func submitTextToImage(ctx context.Context, params aiRequestParams, sess *AISess
 	}
 	defer completeBalanceUpdate(sess.BroadcastSession, balUpdate)
 
+	start := time.Now()
 	resp, err := client.TextToImageWithResponse(ctx, req, setHeaders)
+	took := time.Since(start)
 	if err != nil {
 		return nil, err
 	}
@@ -108,6 +110,13 @@ func submitTextToImage(ctx context.Context, params aiRequestParams, sess *AISess
 		balUpdate.Status = ReceivedChange
 	}
 
+	// TODO: Refine this rough estimate in future iterations
+	numImages := 1
+	if req.NumImagesPerPrompt != nil {
+		numImages = *req.NumImagesPerPrompt
+	}
+	sess.LatencyScore = took.Seconds() / float64(outPixels) / float64(numImages)
+
 	return resp.JSON200, nil
 }
 
@@ -168,7 +177,9 @@ func submitImageToImage(ctx context.Context, params aiRequestParams, sess *AISes
 	}
 	defer completeBalanceUpdate(sess.BroadcastSession, balUpdate)
 
+	start := time.Now()
 	resp, err := client.ImageToImageWithBodyWithResponse(ctx, mw.FormDataContentType(), &buf, setHeaders)
+	took := time.Since(start)
 	if err != nil {
 		return nil, err
 	}
@@ -183,6 +194,9 @@ func submitImageToImage(ctx context.Context, params aiRequestParams, sess *AISes
 		balUpdate.Status = ReceivedChange
 	}
 
+	// TODO: Refine this rough estimate in future iterations
+	sess.LatencyScore = took.Seconds() / float64(outPixels)
+
 	return resp.JSON200, nil
 }
 
@@ -246,7 +260,9 @@ func submitImageToVideo(ctx context.Context, params aiRequestParams, sess *AISes
 	}
 	defer completeBalanceUpdate(sess.BroadcastSession, balUpdate)
 
+	start := time.Now()
 	resp, err := client.ImageToVideoWithBody(ctx, mw.FormDataContentType(), &buf, setHeaders)
+	took := time.Since(start)
 	if err != nil {
 		return nil, err
 	}
@@ -271,6 +287,9 @@ func submitImageToVideo(ctx context.Context, params aiRequestParams, sess *AISes
 		return nil, err
 	}
 
+	// TODO: Refine this rough estimate in future iterations
+	sess.LatencyScore = took.Seconds() / float64(outPixels)
+
 	return &res, nil
 }