Fixes incorrect casting into int for numbers in string format (#384)

tests/server/fastmcp/test_func_metadata.py

@@ -399,3 +399,18 @@ def test_complex_function_json_schema():
         "title": "complex_arguments_fnArguments",
         "type": "object",
     }
+
+
+def test_str_vs_int():
+    """
+    Test that string values are kept as strings even when they contain numbers,
+    while numbers are parsed correctly.
+    """
+
+    def func_with_str_and_int(a: str, b: int):
+        return a
+
+    meta = func_metadata(func_with_str_and_int)
+    result = meta.pre_parse_json({"a": "123", "b": 123})
+    assert result["a"] == "123"
+    assert result["b"] == 123