Make MyPy happy

Fixes for various type errors throw by mypy.

portal/problem_details.py

@@ -2,9 +2,12 @@
 Provide RFC 7807-compliant problem details responses for the API.
 """
 
-from typing import Optional
+from typing import Any, Optional
 
-ProblemResponse = tuple[dict, int, dict]
+ResponseBody = dict[str, Any]
+HttpStatusCode = int
+HttpHeaders = dict[str, str]
+ProblemResponse = tuple[ResponseBody, HttpStatusCode, HttpHeaders]
 
 
 def unauthorized() -> ProblemResponse: