Fix reordering issue in AzureOpenAiChatModel (spring-projects#4156)

Reordering may occur due to `Flux::flatMap` not providing ordering guarantees; 
`flatMapSequential` addresses this issue.

Fixes spring-projects#4155
Auto-cherry-pick to 1.0.x

Signed-off-by: robinmayerhofer <[email protected]>

Author: robinmayerhofer

models/spring-ai-azure-openai/src/main/java/org/springframework/ai/azure/openai/AzureOpenAiChatModel.java

@@ -351,7 +351,7 @@ public Flux<ChatResponse> internalStream(Prompt prompt, ChatResponse previousCha
 							MergeUtils::mergeChatCompletions);
 					return List.of(reduce);
 				})
-				.flatMap(mono -> mono);
+				.flatMapSequential(mono -> mono);
 
 			final Flux<ChatResponse> chatResponseFlux = accessibleChatCompletionsFlux.map(chatCompletion -> {
 				if (previousChatResponse == null) {
@@ -377,7 +377,7 @@ public Flux<ChatResponse> internalStream(Prompt prompt, ChatResponse previousCha
 				return chatResponse1;
 			});
 
-			return chatResponseFlux.flatMap(chatResponse -> {
+			return chatResponseFlux.flatMapSequential(chatResponse -> {
 				if (this.toolExecutionEligibilityPredicate.isToolExecutionRequired(prompt.getOptions(), chatResponse)) {
 					// FIXME: bounded elastic needs to be used since tool calling
 					// is currently only synchronous