Simplify protocol map definitions with function types

[NoamLoewenstern]

Was redirected to this repo after a discussion in a similar repo, realizing where webext-core got inspired from (your repo ;-) )
After opening an issue there and simplifying the ProtocolMap definiotion when using function-types, I would recommend doing the same here.
References to the issue & pull request & change in the other repo, which can be helpful for this repo too:
The original issue
The pull request
The change

And here's a changes I would ask and recommend to modify in types.ts:

export type GetDataType<
  K extends DataTypeKey,
  Fallback extends JsonValue = undefined,
> = K extends keyof ProtocolMap
  ? ProtocolMap[K] extends (...args: infer Args) => any
    ? Args['length'] extends 0
      ? undefined
      : Args[0]
    : ProtocolMap[K] extends ProtocolWithReturn<infer Data, any>
      ? Data
      : ProtocolMap[K]
  : Fallback;


export type GetReturnType<
  K extends DataTypeKey, 
  Fallback extends JsonValue = undefined
> = K extends keyof ProtocolMap
  ? ProtocolMap[K] extends (...args: any[]) => infer Return
    ? Return
    : ProtocolMap[K] extends ProtocolWithReturn<any, infer Return>
      ? Return
      : void
  : Fallback;

[zikaari]

Thanks for reporting, this part of the code was entirely written by another collaborator, I don't have a strong grasp on the how's and what's of this mechanism.

Would you be willing to create a pull request with the proposed changes?

[NoamLoewenstern]

Thanks for reporting, this part of the code was entirely written by another collaborator, I don't have a strong grasp on the how's

Sure. hopefully today, maybe within the next few days.