retry: share one backon helper for the client secret reads and convert the remaining doubling tables

hive-sock-client/Cargo.toml

@@ -16,7 +16,13 @@ workspace = true
 
 [dependencies]
 anyhow.workspace = true
+backon.workspace = true
 serde.workspace = true
 serde_json.workspace = true
 tokio.workspace = true
 tracing.workspace = true
+
+[dev-dependencies]
+# `test-util` for `#[tokio::test(start_paused = true)]`: the ride-out test
+# waits out the whole schedule on paused time.
+tokio = { workspace = true, features = ["test-util"] }