fix: support strands-agents >= 1.16 by using explicit Optional types

[kevmyung]

• Remove 'from future import annotations' to fix forward reference issues
• Use Optional[T] instead of T | None for Pydantic compatibility
• Remove upper bound on strands-agents version

Issue #, if available:
Fixes #89

Description of changes:
from future import annotations(PEP 563) causes forward reference issues with strands-agents >= 1.16's@tool` decorator when generating Pydantic models.

Error:
PydanticUserError: Agent_clickTool is not fully defined;
you should define ClickType, then call Agent_clickTool.model_rebuild().

Solution

• Remove from __future__ import annotations to fix forward reference issues
• Use Optional[T] instead of T | None for Pydantic compatibility
• Remove upper bound on strands-agents version

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