fix: allow structured results in tool-end hooks

[he-yufeng]

Summary

• change RunHooksBase.on_tool_end and AgentHooksBase.on_tool_end to accept structured tool results
• add regression coverage for dict-valued function tool results reaching both run-level and agent-level hooks

Fixes #3512

To verify

• uv run pytest tests/test_run_hooks.py -q
• uv run pytest tests/test_agent_hooks.py tests/test_agent_llm_hooks.py tests/test_global_hooks.py tests/test_computer_action.py tests/test_run_step_execution.py -q
• uv run ruff check src/agents/lifecycle.py tests/test_run_hooks.py tests/test_agent_hooks.py tests/test_agent_llm_hooks.py tests/test_global_hooks.py tests/test_computer_action.py tests/test_run_step_execution.py
• uv run ruff format --check src/agents/lifecycle.py tests/test_run_hooks.py tests/test_agent_hooks.py tests/test_agent_llm_hooks.py tests/test_global_hooks.py tests/test_computer_action.py tests/test_run_step_execution.py
• uv run mypy src/agents/lifecycle.py tests/test_run_hooks.py tests/test_agent_hooks.py tests/test_agent_llm_hooks.py tests/test_global_hooks.py tests/test_computer_action.py tests/test_run_step_execution.py
• uv run pyright --project pyrightconfig.json src/agents/lifecycle.py tests/test_run_hooks.py tests/test_agent_hooks.py tests/test_agent_llm_hooks.py tests/test_global_hooks.py tests/test_computer_action.py tests/test_run_step_execution.py

[seratch]

Thanks for sharing this. Resolved by #3518