Enum generics

The Enum base class has 3 type arguments.

Type argument	Description	Default
`V`	The variant type.	REQUIRED
`K`	Current variant key.	`unknown`
`NV`	Narrowed variant value.	`V[K]` or `V[keyof K]`

export class Enum<
  V,
  K extends EnumNarrowSelector<V> = unknown,
  NV extends V[keyof V] = K extends keyof V ? V[K] : V[keyof V]
> {
  #variant: K;
  #value: NV;

  // ...
}