fix: export ApplyPatchTool and CustomTool approval callback types from top-level package

[rmotgi1227]

ApplyPatchTool and CustomTool each accept an on_approval callback, and ComputerTool accepts an on_safety_check callback. The types needed to annotate those callbacks are not exported from the top-level agents package:

• ApplyPatchOnApprovalFunction / ApplyPatchOnApprovalFunctionResult
• CustomToolOnApprovalFunction / CustomToolOnApprovalFunctionResult
• ComputerToolSafetyCheckData

The equivalent MCP types (MCPToolApprovalFunction, MCPToolApprovalFunctionResult) are already exported. This extends that to the remaining tool types.

# currently breaks — have to reach into private agents.tool module:
from agents import ComputerToolSafetyCheckData   # ImportError
from agents import ApplyPatchOnApprovalFunction  # ImportError
from agents import CustomToolOnApprovalFunction  # ImportError

Related to #3450 which exports the Shell equivalents.

[seratch]

hmm, we'd like to hold off adding these as they are not commonly used plus developers can still import from agents.tool.