fix(anthropic): type the decoded JSON mode answer as object and test non-object answers

Backport of #50470 to lts/1.108.x.
Cherry-picked from 6809224df9 (litellm_fix_anthropic_stream_fragment_json).

litellm/llms/base_llm/base_utils.py

@@ -229,7 +229,9 @@ def _is_decoded_json_object(
 
 def decoded_answer_object(text: str) -> Mapping[str, AnswerValue] | None:
     try:
-        decoded: Final[object] = json.loads(text, parse_float=_source_float, parse_int=_source_int)
+        decoded: Final = _DECODED_JSON.validate_python(
+            json.loads(text, parse_float=_source_float, parse_int=_source_int)
+        )
     except (json.JSONDecodeError, RecursionError):
         return None
     return decoded if _is_decoded_json_object(decoded) else None

tests/unit/llms/anthropic/chat/test_anthropic_chat_handler.py

@@ -2958,6 +2958,9 @@ _DIGITS_PAST_THE_INT_LIMIT: Final = "1" * (sys.get_int_max_str_digits() + 1)
         (('{"n": 1e5}',), '{"n": 1e5}'),
         (('{"values": false}',), "false"),
         (('{"values": null}',), '{"values": null}'),
+        (("[1, 2]",), "[1, 2]"),
+        (('"x"',), '"x"'),
+        (("5",), "5"),
         pytest.param(
             ('{"values": ' + "[" * 300 + "]" * 300 + "}",),
             "[" * 300 + "]" * 300,

tests/unit/llms/anthropic/chat/test_anthropic_chat_transformation.py

@@ -7909,6 +7909,24 @@ def test_convert_tool_response_to_message_keeps_arguments_too_deep_to_decode(arg
     assert message.content == arguments
 
 
+@pytest.mark.parametrize("arguments", ["[1, 2]", '"x"', "5"])
+def test_convert_tool_response_to_message_keeps_a_non_object_answer_as_written(arguments: str) -> None:
+    message: Final = AnthropicConfig.convert_tool_response_to_message(
+        tool_calls=[
+            ChatCompletionToolCallChunk(
+                id="toolu_1",
+                type="function",
+                function=ChatCompletionToolCallFunctionChunk(name=RESPONSE_FORMAT_TOOL_NAME, arguments=arguments),
+                index=0,
+            )
+        ],
+        response_format_schema=None,
+    )
+
+    assert message is not None
+    assert message.content == arguments
+
+
 _DEEPLY_NESTED: Final = "[" * 300 + "]" * 300
 
 
@@ -7926,7 +7944,7 @@ _DEEPLY_NESTED: Final = "[" * 300 + "]" * 300
 )
 def test_convert_tool_response_to_message_unwraps_a_deeply_nested_answer(
     arguments: str, schema: dict[str, object] | None, expected: str
-):
+) -> None:
     message = AnthropicConfig.convert_tool_response_to_message(
         tool_calls=[
             ChatCompletionToolCallChunk(