Fix & re-enable rs-wnfs integration tests

[matheus23]

Fixes #429

I added the "no changelog" label since this is only a fix for a feature behind an experimental feature flag. I don't think this needs a changelog entry. Right?

[matheus23]

I wrote more about the issue itself here:

rustwasm/wasm-bindgen#3307

[matheus23]

So apparently, the original code already had that initialized variable which prevents the bug:
https://github.com/fission-codes/webnative/blob/2d0a93e4f435a51a7618ce47544fb17b391352ad/src/fs/v3/PublicRootWasm.ts#L19-L22

But then it got reverted in https://github.com/fission-codes/webnative/pull/422/files?diff=unified&w=0#diff-4952ebe25ed816f4c8f9f5d03618522f41ab5e00941e4a69f46990b1f9755094L19-R28

This is just reverting the revert.

I realize the refactor's goal when it removed the initialized variable tried to get rid of global mutable state in general. Unfortunately, in this case we can't get rid of it, as we need to be careful about correctly maintaining wasm-bindgen-generated code (which contains global mutable state), and which is somewhat out of our control. The best we can do is file an issue (see the previous message).

So, I added more comments signalling that this code must not be deleted.

[icidasset]

Thanks! 🙏