fix: stack overflow when config have both default and named exports

[astrochemx]

Description

🧩 Backstory

After the 7.4.0 update, a Maximum call stack size exceeded error started to occur when using taze, that started throwing errors with configurations that export both default and named exports simultaneously.

🐛 Issue

After some debugging, I traced the issue back to this change, which introduced the faulty behavior. As I understand, interopDefault function tries to create a getter for the self-referential default key and/or for the module property which already is the default object. This results in defining a self-referential getter (defaultValue.default → mod.default → defaultValue), which leads to infinite recursion when Node attempts to inspect or log the object, ultimately triggering the stack overflow.

✔️ Fix

This PR prevents processing the default key or the module property which already is the default object when defining forwarded getters. By skipping these, we avoid creating a self-referential properties and eliminate the infinite recursion.

🧪 Tests

All existing tests have passed.
Also, I’ve added several new tests covering the main scenarios that previously triggered the recursion.

🧾 Reproduction

unconfig-repro

Additional context

I’m not deeply familiar with the internal design of unconfig and its ecosystem, so the approach may not be ideal.
Feedback and further refinements are very welcome.