Resuming an object operation produces confusing error message

[jiribenes]

I was playing around with objects and managed to write resume( ... ) by accident. This however produced a very confusing error message about not being able to infer the type of the continuation.

I think that we should be able to special-case this and produce a more relevant message to the user.

I believe this is the relevant line of code throwing the error message -- it might be helpful to check continuationDetails https://github.com/effekt-lang/effekt/blob/471f9da2380dac9cd2d057d12cad60496cc20bb3/effekt/shared/src/main/scala/effekt/Typer.scala#L317

[b-studios]

+1 This is a wellformedness check that should report something useful like "resuming is only supported in effect handlers, not when defining objects.".

Ideally, this should be done in Namer, I believe. Maybe in

https://github.com/effekt-lang/effekt/blob/471f9da2380dac9cd2d057d12cad60496cc20bb3/effekt/shared/src/main/scala/effekt/Parser.scala#L564

we should only synthesize resume, if we are actually in a handler?