Do not set `global.self` if not needed

Hi,
We have a node CLI that uses threads.js, and discovered that global.self is being set by the library although it's not needed.
It is always being set here, even if the tiny-worker implementation is not needed:

threads.js/src/worker/implementation.tiny-worker.ts

Lines 14 to 16 in 545baa2

    
           if (typeof self === "undefined") { 
        
             (global as any).self = global 
        
           }

This happens because it is always imported and the code is running on the module level.

This causes other 3rd party code we have to assume it's running in a browser. There might be a better way for the 3rd party to detect whether it's in a browser, although I think regardless we should not set self if not needed.

Would love to hear your thoughts, thanks!

	if (typeof self === "undefined") {
	(global as any).self = global
	}