fix: Use correct format when resolving exports from sub-modules

[timfish]

Closes #139

When we resolve sub-modules to get their exports, parentResolve can return a different format to the current module type and this should be used when loading the module source!

This change is potnetially a one-liner but I refactored the code a bit to avoid initially setting let variables as undefined only to set them later in an if/else.

[AbhiPrasad]

the differing formats is really tricky, something we need to keep an eye on for the future.