ClientRpc and ServerRpc decorators should give an error if attached to a non-NetworkBehaviour class method

Is your feature request related to a problem? Please describe.
I'm finding it easy to accidentally add [ClientRpc] or [ServerRpc] methods to MonoBehaviour-derived classes, where clearly they won't do anything. This leads to a bunch of confusion while I try to figure out what's wrong with the networking only to do the forehead-slap when I notice that the class hasn't been switched to NetworkBehaviour.

Describe the solution you'd like
At a minimum, a runtime error with a descriptive error message would be helpful. Something like "FooClientRpc was added to a class that doesn't derive from NetworkBehaviour - as a result, FooClientRpc will never be called."

Better would be a similar error logged when in the editor. Compile-time errors would be ideal if possible, of course.

Describe alternatives you've considered
Beyond "vigilance" (which can be assumed doesn't work), if it becomes a more serious issue then I'd have to rig some sort of linting rule to catch this.

The issue does not name files, tests, or entry points. Start by locating the ClientRpc and ServerRpc decorator handling and how NetworkBehaviour inheritance is checked; define and test a diagnostic for methods on classes that do not derive from NetworkBehaviour, including the requested runtime or editor behavior.