standardize packaging, tooling, docs, CI, and licensing

mail_intake/credentials/pickle.py

@@ -16,7 +16,7 @@ untrusted environments.
 """
 
 import pickle
-from typing import Optional, TypeVar
+from typing import TypeVar
 
 from mail_intake.credentials.store import CredentialStore
 
@@ -55,7 +55,7 @@ class PickleCredentialStore(CredentialStore[T]):
         """
         self.path = path
 
-    def load(self) -> Optional[T]:
+    def load(self) -> T | None:
         """
         Load credentials from the local filesystem.