Python: fix: resolve string annotations in FunctionExecutor (#2308)

* fix: resolve string annotations in FunctionExecutor

Enhance type hint validation in FunctionExecutor by importing `typing` and
using `get_type_hints` to correctly resolve annotations.

This fixes validation failures when `from __future__ import annotations`
is enabled, which stores annotations as strings.

Fixes #1808

* Update python/packages/core/tests/workflow/test_function_executor_future.py

Co-authored-by: Copilot <175728472+Copilot@users.noreply.github.com>

* ran pre commit

---------

Co-authored-by: Copilot <175728472+Copilot@users.noreply.github.com>

python/packages/core/tests/workflow/test_function_executor_future.py

@@ -0,0 +1,39 @@
+# Copyright (c) Microsoft. All rights reserved.
+
+from __future__ import annotations
+
+from typing import Any
+
+from agent_framework import FunctionExecutor, WorkflowContext, executor
+
+
+class TestFunctionExecutorFutureAnnotations:
+    """Test suite for FunctionExecutor with from __future__ import annotations."""
+
+    def test_executor_decorator_future_annotations(self):
+        """Test @executor decorator works with stringified annotations."""
+
+        @executor(id="future_test")
+        async def process_future(value: int, ctx: WorkflowContext[int]) -> None:
+            await ctx.send_message(value * 2)
+
+        assert isinstance(process_future, FunctionExecutor)
+        assert process_future.id == "future_test"
+        assert int in process_future._handlers
+
+        # Check spec
+        spec = process_future._handler_specs[0]
+        assert spec["message_type"] is int
+        assert spec["output_types"] == [int]
+
+    def test_executor_decorator_future_annotations_complex(self):
+        """Test @executor decorator works with complex stringified annotations."""
+
+        @executor
+        async def process_complex(data: dict[str, Any], ctx: WorkflowContext[list[str]]) -> None:
+            await ctx.send_message(["done"])
+
+        assert isinstance(process_complex, FunctionExecutor)
+        spec = process_complex._handler_specs[0]
+        assert spec["message_type"] == dict[str, Any]
+        assert spec["output_types"] == [list[str]]