perf: opt out instance_init for bool and enum

Author: maartenbreddels

traitlets/traitlets.py

@@ -2616,6 +2616,9 @@ def from_string(self, s):
         else:
             raise ValueError("%r is not 1, 0, true, or false")
 
+    def subclass_init(self, cls):
+        pass  # fully opt out of instance_init
+
 
 class CBool(Bool):
     """A casting version of the boolean trait."""
@@ -2667,6 +2670,9 @@ def from_string(self, s):
         except TraitError:
             return _safe_literal_eval(s)
 
+    def subclass_init(self, cls):
+        pass  # fully opt out of instance_init
+
 
 class CaselessStrEnum(Enum):
     """An enum of strings where the case should be ignored."""