fix(mypy): resolve provider utility and testing type issues

Fixes mypy type errors across provider utilities and testing infrastructure (Phase 2e):

- mcp.py (2 errors fixed):
  - Cast sse_client to Any to handle incompatible signatures with streamablehttp_client
  - Wrap ImageContent data in _URLOrData(data=...) for proper ImageContentItem construction

- batches.py (1 error fixed):
  - Rename walrus operator variable from `body` to `request_body` to avoid shadowing
    the file content `body` variable (bytes|memoryview) defined earlier in scope

- api_recorder.py (1 error fixed):
  - Cast Pydantic field annotation assignment to proper type when monkey-patching
    OpenAI CompletionChoice model to accept None in finish_reason

Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude <noreply@anthropic.com>

src/llama_stack/providers/inline/batches/reference/batches.py

@@ -419,8 +419,8 @@ class ReferenceBatchesImpl(Batches):
                         )
                         valid = False
 
-                    if (body := request.get("body")) and isinstance(body, dict):
-                        if body.get("stream", False):
+                    if (request_body := request.get("body")) and isinstance(request_body, dict):
+                        if request_body.get("stream", False):
                             errors.append(
                                 BatchError(
                                     code="streaming_unsupported",