Effects should not be displayed when empty

[b-studios]

When hovering over a function its full return type and effects are shown.

This is in contrast to our usual presentation where we would omit the empty set of effects and just say show returns a String (but not String / {}).

The code that renders function declarations is here:

effekt/effekt/shared/src/main/scala/effekt/symbols/DeclPrinter.scala

Lines 86 to 89 in 80467d8

	val returnType = for {
	tpe <- result
	eff <- effects
	} yield pp": $tpe / $eff"

and should be adapted to print effects similar to the TypePrinter:

effekt/effekt/shared/src/main/scala/effekt/symbols/TypePrinter.scala

Line 76 in 80467d8

val eff = if (effects.isEmpty) emptyDoc else space <> "/" <+> toDoc(effects)

Optional: Maybe some logic between TypePrinter and DeclPrinter can be deduplicated

[jiribenes]

I sort of like this though as it's explicit about the effects a function has.
But I'm fine with removing it.