Updated dUSD spec based on Ryan's requests

other changes

[ ] The impure tests via nix run .#offchain:test were run and all are passing.
[ ] Where applicable, grammar, punctuation, and spelling within code and comments should be plausibly correct.
[ ] The issue(s) that the work is addressing should be linked in the PR description.
[ ] Any significant changes beyond what's clear from the linked issue(s) are documented in the PR description

ArdanaLabs / dUSD