examples: add a streaming tool-calling example

[Rohan5commit]

Summary

• add a dedicated streaming example that accumulates tool call chunks and then sends the tool result back to the model
• keep the example in examples/, which CONTRIBUTING.md marks as a safe manually maintained surface

Related issue

• Closes Want an example of streaming with tool calling #402

Guideline alignment

• keeps the change to a single example file with no library behavior changes
• uses the existing chat-completions example style and focuses on one concrete streaming tool-calling flow

Validation

• ran git diff --check

[Copilot]

Pull request overview

Adds a new Go example demonstrating streaming Chat Completions with tool calling, including accumulating streamed tool-call argument chunks and then sending tool results back to the model for a final response.

Changes:

• Add examples/chat-completion-tool-calling-streaming/main.go showcasing a full streaming → tool execution → follow-up completion flow
• Demonstrate use of ChatCompletionAccumulator with JustFinishedToolCall() to detect completed tool calls during streaming

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[Copilot]

The loop skips any tool calls whose name isn’t get_weather, but still proceeds to make the follow-up Chat.Completions.New call. If the model ever returns an unexpected tool call (or if this example is later extended with additional tools), this will send an assistant message containing unresolved tool calls and can cause the next request to fail (e.g., missing tool result for a tool_call_id). Prefer failing fast (panic/return with an error) for unknown tool names, or ensure you append a tool result message for every tool call in acc.Choices[0].Message.ToolCalls.

Suggested change

	continue
	panic(fmt.Sprintf("unexpected tool call %q (id=%s)", toolCall.Function.Name, toolCall.ID))

[Copilot]

acc.AddChunk(chunk) can return false when a mismatch is detected (e.g., chunk IDs changing mid-stream). Panicking with a generic string makes debugging harder; consider including relevant context (e.g., accumulated ID vs chunk.ID) or panicking with a formatted error so users can quickly understand what went wrong.

Suggested change

	panic("failed to accumulate stream chunk")
	panic(fmt.Sprintf("failed to accumulate stream chunk: accumulator ID %q does not match chunk ID %q", acc.ID, chunk.ID))