apt: query the Launchpad PPA API through the shared HTTP client

src/launchpad.rs

@@ -92,8 +92,9 @@ fn person_url(user: &str) -> String {
 }
 
 /// URL of the Launchpad API resource of a PPA (`~user/+archive/ubuntu/name`
-/// covers the default `ppa` archive and named archives alike)
-fn archive_url(user: &str, ppa: &str) -> String {
+/// covers the default `ppa` archive and named archives alike); shared by the
+/// put-side pre-flight checks and the apt keyring's fingerprint lookup
+pub(crate) fn archive_url(user: &str, ppa: &str) -> String {
     format!("{API_BASE}/~{user}/+archive/ubuntu/{ppa}")
 }