🐛 Fixes BSN support for fully qualified component paths

[ekwoka]

Objective

Currently using fully qualified paths in bsn! fails compilation

bsn! {
  ::bevy::ui::Node
}

This is due to the parser seeing the : token and immediately going to the scene parsing path.

Solution

Check that the token isn't part of :: when checking for that branch.

Testing

There didn't seem to be any testing of the actual macro parsing (that I could find) so I put a simple test that just makes sure it compiled and produces a valid scene, though doesn't check that the scene is ACTUALLY "correct".

[ekwoka]

Or...should this also handle ::: being cache + fully qualified? Does caching work with any identifiers?

[ekwoka]

Actually, seems ::: works fine as : :: for the purpose of caching a fully qualified scene function