When processing `input_json_delta` events, the Anthropic client was
passing the tool name from the previous `tool_use` event. This caused
ag-ui's `_handle_function_call_content` to emit a `ToolCallStartEvent`
for every streaming chunk (since it triggers on `if content.name:`).
This fix changes the behavior to pass an empty string for `name` in
`input_json_delta` events, matching OpenAI's behavior where streaming
argument chunks have `name=""`. The initial `tool_use` event still
provides the tool name, so only one `ToolCallStartEvent` is emitted.
Co-authored-by: Evan Mattson <35585003+moonbox3@users.noreply.github.com>
