Advisory endpoint an ISV can call before creating a user. The submitted
address is sent to Smarty for validation/normalization. On success the
normalized address is returned along with a status:
verified (input already matched exactly), corrected (normalized and
changed), or missing_secondary (deliverable but missing an apartment/
suite number). If Smarty cannot find the address, responds 422 with code
address_not_found. Does not create a user or persist anything.

US addresses only (Smarty US Street Address API).