TSL: Missing overload for Fn and incorrect Node typing

[stofi]

Description

Declaring a Fn function without a Node return type throws a TypeScript error:

const computeFn = Fn(() => {}); 
// Error: Argument of type '() => void' is not assignable to parameter of type '() => Node'.

This results in a computeFn having an incorrect type, leading to further type errors when attempting to compute the function:

const computeNode = computeFn().compute();
// Error: Property 'compute' does not exist on type 'Node'.

It seems to only affects the type, the actual code runs without issues.

This issue was also mention on the Three.js discourse forum:
https://discourse.threejs.org/t/are-there-any-up-to-date-webgpu-169-examples/73378

I am willing to work on a pull request to fix this issue.

Environment:

"@types/three": "0.171"
"three": "0.171"
"typescript": "5.6.2"
"vite": "6.0.1"

Reproduction

A minimal reproducible example is available here:
https://github.com/stofi/three-types-tsl-fn-repro

[Methuselah96]

Feel feel to create a PR