`isolatedDeclarations` is not yet implemented

[so1ve]

Steps to reproduce

(I'm unable to create a minimal reproduction now, sorry, I'll create one if I'm available)

Steps:

1. enable isolatedDeclarations in tsconfig.isolated.json
2. write code like expprt const foo = (() => 1)()
3. run tsgo -p tsconfig.isolated.json --noEmit

Behavior with typescript@5.9

tsc -p tsconfig.isolated.json --noEmit throws an error, prompting an annotation is needed.

Behavior with tsgo

nothing happened