perf: make silverback --help faster (#162)

setup.cfg

@@ -1,5 +1,6 @@
 [flake8]
 max-line-length = 100
+ignore = E704,W503,PYD002
 exclude =
 	venv*
 	.eggs

silverback/__init__.py

@@ -1,6 +1,24 @@
-from .exceptions import CircuitBreaker, SilverbackException
-from .main import SilverbackBot
-from .state import StateSnapshot
+def __getattr__(name: str):
+    if name == "CircuitBreaker":
+        from .exceptions import CircuitBreaker
+
+        return CircuitBreaker
+
+    elif name == "SilverbackException":
+        from .exceptions import SilverbackException
+
+        return SilverbackException
+
+    elif name == "SilverbackBot":
+        from .main import SilverbackBot
+
+        return SilverbackBot
+
+    elif name == "StateSnapshot":
+        from .state import StateSnapshot
+
+        return StateSnapshot
+
 
 __all__ = [
     "StateSnapshot",