Replace the inline cookie split with stealth_bitcoincore::read_cookie_file,
which already implements the same parsing with proper error handling.
Removes duplication and keeps the cookie format in one place.
The if-chain and counter pattern is a 5-arm tuple match in disguise.
Pattern match on (descriptor, descriptors, utxos) directly: every
valid case picks exactly one variant, the empty tuple is a clear
missing-input error, and the wildcard catches mutual-exclusion
violations.
Browser-based frontends need CORS to call the API. Apply
tower_http::cors::CorsLayer::permissive() at the router level so
the frontend (and other origins during development) can reach the
scan endpoint.
LORDBABUINO