Fix: handle JSON parse error in streaming tool calls

[kmw10693]

Overview

This PR fixes a JSON parsing error that occurs when handling streaming tool calls in Spring AI.

Related issue: spring-projects/spring-ai#4250

---

Why

• In streaming mode, tool call JSON fragments can arrive incomplete.
• This results in Jackson throwing errors such as: com.fasterxml.jackson.core.JsonParseException: Unexpected close marker ']': expected '}'
• The issue only occurs in streaming (stream()) calls.
• Synchronous calls (call()) are not affected.
• This prevents users from reliably using tool callbacks with streaming responses.

---

What Changed

• Added a new ToolExecutionEligibilityPredicate implementation: ToolOnFinishPredicate.
• Ensures tool execution only runs after the assistant signals completion (finishReason = "tool_calls" or "stop").
• Prevents premature execution and malformed JSON during streaming tool calls.

---

How to Use

Example usage:

ChatClient client = ChatClient.create(openAiChatModel);

String result = client.prompt()
  .user("Migrate node cluster xx")
  .toolCallbacks(ToolCallbacks.from(new MyTool()))
  .options(OpenAiChatOptions.builder()
      .toolExecutionEligibilityPredicate(new ToolOnFinishPredicate())
      .build())
  .stream()
  .content();

[markpollack]

can't use this annotation for not null

[markpollack]

The PR looks incomplete. I've commented on the issue thread for further clarification. #4274