perf: stop the sweep stealing worker wakeups, retry-free inline fetch

- queue: the lease-expiry sweep waited on the workers' `Notify`. `notify_one`
  stores a permit, so a sweep wakeup could consume the one meant for a worker,
  which then blocked on `notified()` (it only waits when the table looked
  empty, i.e. indefinitely) with a due row sitting there. The sweep now has
  its own notify, woken only by stop.
- x-media: split fetch's retry loop into `fetch` (3 attempts, unchanged) and
  `fetch_once` (1 attempt); inline queries use the latter — the 800ms debounce
  plus 1s/2s backoffs were outlasting the answer window of the query.
- send: chunk_media_items now moves items out of the input Vec instead of
  requiring `T: Clone` and copying every payload.

fmt/clippy clean, 55 + 69 tests pass.

crates/x-media/src/site/mod.rs

@@ -375,10 +375,24 @@ pub async fn validate_all() -> Vec<(&'static str, String)> {
 /// are returned immediately; retrying them only wastes attempts against the
 /// source site.
 pub async fn fetch(url: &str) -> Result<Option<Fetched>, FetchError> {
+    fetch_with_attempts(url, MAX_FETCH_ATTEMPTS).await
+}
+
+/// [`fetch`] without the retry backoff (one attempt). For callers with a
+/// short deadline: an inline query's answer window is measured in seconds, so
+/// the 1s + 2s retry sleeps would outlast the query the answer belongs to.
+pub async fn fetch_once(url: &str) -> Result<Option<Fetched>, FetchError> {
+    fetch_with_attempts(url, 1).await
+}
+
+/// Total attempts of the retried [`fetch`] (3: the initial try plus two).
+const MAX_FETCH_ATTEMPTS: u32 = 3;
+
+async fn fetch_with_attempts(url: &str, attempts: u32) -> Result<Option<Fetched>, FetchError> {
     let Some(site) = find_site(url) else {
         return Ok(None);
     };
-    for attempt in 0..3u32 {
+    for attempt in 0..attempts.max(1) {
         match site.fetch_from_url(url).await {
             Ok(fetched) => {
                 // Per-request detail: debug only, keyed by the post id.
@@ -391,7 +405,7 @@ pub async fn fetch(url: &str) -> Result<Option<Fetched>, FetchError> {
                 return Ok(Some(fetched));
             }
             Err(err) => {
-                if site.is_retryable(&err) && attempt < 2 {
+                if site.is_retryable(&err) && attempt + 1 < attempts {
                     tokio::time::sleep(Duration::from_secs(1 << attempt)).await;
                 } else {
                     return Err(err);