Theseus circuit breaker (#5196)

* Impl request fence

* Reduce max FETCH_ATTEMPTS

* Tweak fail threshold & window

* Check block status every retry iteration

* Fix fmt

* Fix fmt 2

packages/app-lib/src/error.rs

@@ -65,6 +65,9 @@ pub enum ErrorKind {
     #[error("Error fetching URL: {0}")]
     FetchError(#[from] reqwest::Error),
 
+    #[error("Too many API errors; temporarily blocked")]
+    ApiIsDownError,
+
     #[error("{0}")]
     LabrinthError(LabrinthError),