standardize packaging, tooling, docs, CI, and licensing

mail_intake/credentials/store.py

@@ -19,9 +19,8 @@ or secrets managers—without coupling authentication logic to any
 specific storage mechanism.
 """
 
-
 from abc import ABC, abstractmethod
-from typing import Generic, Optional, TypeVar
+from typing import Generic, TypeVar
 
 T = TypeVar("T")
 
@@ -48,7 +47,7 @@ class CredentialStore(ABC, Generic[T]):
     """
 
     @abstractmethod
-    def load(self) -> Optional[T]:
+    def load(self) -> T | None:
         """
         Load previously persisted credentials.