refactor: improve intellisense for selector subscriptions

currently if you do not provide explicit type in the selector, then the handler function will have `unknown` params.
This is because TS does not know which generic type to use for `SelectorReturnValue`.

I tried using the `NoInfer` type to prevent the handler function from winning the inference, but unfortunately `NoInfer` does not work with return values.

The other option was to switch the handler fn and selector fn around, however this is a destructive change.

By making the handler fn use its own generics (which are constrained by the original `SelectorReturnValue`), we effectively defer or ensure that the handler doesn't win the inference.

packages/base-controller/src/Messenger.ts

@@ -58,9 +58,12 @@ export type SelectorFunction<
   EventType extends Event['type'],
   ReturnValue,
 > = (...args: ExtractEventPayload<Event, EventType>) => ReturnValue;
-export type SelectorEventHandler<SelectorReturnValue> = (
-  newValue: SelectorReturnValue,
-  previousValue: SelectorReturnValue | undefined,
+export type SelectorEventHandler<SelectorReturnValue> = <
+  // Deferring value as implicit types do not get used correctly
+  DeferredVal = SelectorReturnValue,
+>(
+  newValue: DeferredVal,
+  previousValue: DeferredVal | undefined,
 ) => void;
 
 export type ActionConstraint = {