Return signature on anthropic streaming + migrate to signature field instead of signature_delta [MINOR bump] (#9021)

* Fix missing signature_delta in thinking blocks when streaming from Claude 3.7 (#8797)

Co-authored-by: Krish Dholakia <krrishdholakia@gmail.com>

* test: update test to enforce signature found

* feat(refactor-signature-param-to-be-'signature'-instead-of-'signature_delta'): keeps it in sync with anthropic

* fix: fix linting error

---------

Co-authored-by: Martin Krasser <krasserm@googlemail.com>

tests/local_testing/test_streaming.py

@@ -4084,6 +4084,7 @@ def test_reasoning_content_completion(model):
         )
 
         reasoning_content_exists = False
+        signature_delta_exists = False
         for chunk in resp:
             print(f"chunk 2: {chunk}")
             if (
@@ -4118,3 +4119,4 @@ def test_is_delta_empty():
             audio=None,
         )
     )
+