test: reorganize core suite into explicit domain files

tests/conftest.py

@@ -3,6 +3,7 @@ from __future__ import annotations
 import sys
 from pathlib import Path
 from types import ModuleType
+from typing import Any, cast
 
 
 ROOT = Path(__file__).resolve().parents[1]
@@ -15,21 +16,26 @@ try:
 except ModuleNotFoundError:
     audible_stub = ModuleType("audible")
 
-    class Authenticator:  # minimal stub for type usage
+    class Authenticator:
+        """Minimal audible authenticator test stub."""
+
         pass
 
-    class Client:  # minimal stub for type usage
+    class Client:
+        """Minimal audible client test stub."""
+
         pass
 
-    audible_stub.Authenticator = Authenticator
-    audible_stub.Client = Client
+    setattr(cast(Any, audible_stub), "Authenticator", Authenticator)
+    setattr(cast(Any, audible_stub), "Client", Client)
 
     activation_bytes = ModuleType("audible.activation_bytes")
 
     def get_activation_bytes(_auth: Authenticator | None = None) -> bytes:
+        """Return deterministic empty activation bytes for tests."""
         return b""
 
-    activation_bytes.get_activation_bytes = get_activation_bytes
+    setattr(cast(Any, activation_bytes), "get_activation_bytes", get_activation_bytes)
 
     sys.modules["audible"] = audible_stub
     sys.modules["audible.activation_bytes"] = activation_bytes