Resolves issue: solidusio#4270

Some tests were modified to give a state with the address parameters
as they used a country which will now get the states_required attribute
of true, meaning a state must be present on the address.

Improves the readability of the next commit.

For some countries such as Italy, its states are nested within regions,
and not at the first level of subregions like 'US'.
`country > region > states`
`Carmen::Country.coded('IT').subregions.first.type`

Now nested subregions exist, it will use this instead. This will be
useful for when using the state factory, but also necessary for the
upcoming commit, where if a state is not given, but a country is, for
the address factory, it can automatically use/create the first state of
that country.

Two rationales for this change:
1. Now that the states_required attribute is now functioning in the
  country factory, some specs for codebases might start breaking, due to
  them using an address factory, not giving a state, but using a country
  that requires a state. This should prevent many breaking tests *
2. Less setup is now needed for specs. Only a state or country is needed
   for a valid non-US (default) address

* But not all, for example address API endpoint specs might break, which
happened for Solidus:
cf84832