docs: clarify on_tool_start and on_tool_end hooks for local tools only

[ihower]

This PR improves the doc comments for the on_tool_start and on_tool_end hooks.

Clarified that these hooks are for local tools only, and do not include hosted tools running on the OpenAI server side (e.g., WebSearchTool, FileSearchTool, CodeInterpreterTool, HostedMCPTool, etc.).

Related Issues

• web_search_preview never triggers agents.lifecycle.AgentHooks.on_tool_start #778 rm-openai said: “I should document this better”, this PR addresses that note.
• WebSearchTool no LifeCycle Events on Agent via AgentHook subclass #1889
• Feature Request: Support all AgentHooks when Agent.as_tool() #2036

[seratch]

Thanks! This is a really nice improvement

[hayescode]

Thank you @ihower ! @seratch any plans to support these hooks for hosted tools? Responses API seems to have create/delta/completed events for all tools, hosted and local, and particularly for MCP servers with lots of tools we don't have a way to see what MCP tools were called, their arguments, outputs, etc. at least for Agent.as_tool().

[seratch]

@hayescode when you use streaming, it may be possible to relay those events to the agent lifecycle hooks. But for developers who use non-streaming mode, it's not yet feasible to support the same. in the short term, enabling those hooks only for streaming mode could be indeed a good feature addition on this SDK side (although I myself haven't verified if it's really feasible without any restrictions).