Look at a feed's artwork only when it may have changed, and trace a scan's database work (#95, #96)

A feed read in full checked its own artwork and, without one, asked its website for an icon,
every time; a feed without validators is read in full every scan, so looking-for-group spent
2 s of every scan loading lfg.co's home page. Now the check runs when the feed names different
artwork from what is stored, or the scan was asked for, which keeps #80's point: a refresh
still picks up an icon the site changes or fixes.

Feed spans ran seconds past their fetch with nothing to say where (#96). The artwork lookup,
the loop that stores each item, and the per-feed database calls (feed_summary, record_feed,
subscribers, adopt, skipped_by_filter, rehide, pending) now have spans of their own.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

src/db.rs

@@ -313,6 +313,7 @@ impl Db {
         Ok(())
     }
 
+    #[tracing::instrument(skip_all)]
     pub async fn feed_summary(&self, feed_id: &str) -> Result<FeedSummary> {
         let mut sum = feeds::Entity::find_by_id(feed_id.to_owned())
             .one(&self.orm)
@@ -432,6 +433,7 @@ impl Db {
 
     /// Upsert after a successful poll. Clears any previous error.
     #[allow(clippy::too_many_arguments)]
+    #[tracing::instrument(skip_all)]
     pub async fn record_feed(
         &self,
         feed_id: &str,
@@ -623,6 +625,7 @@ pub struct Pending {
 impl Db {
     /// The download queue is the table, not the parse result: an enclosure held back by
     /// `max_new_per_check` is simply picked up by the next scan, in feed order.
+    #[tracing::instrument(skip_all)]
     pub async fn pending(&self, feed_id: &str, limit: usize) -> Result<Vec<Pending>> {
         // Newest first: a cap of 3 should mean the three latest episodes, not the three that
         // happen to have been recorded first.
@@ -1191,6 +1194,7 @@ impl Db {
     /// and downloads, since one file serves the lot.
     /// In a group, whatever someone has not set on the feed itself comes from their
     /// subscription to the group, as the group's settings dialog has always said it does.
+    #[tracing::instrument(skip_all)]
     pub async fn subscribers(&self, feed_id: &str, group: Option<&str>) -> Result<Vec<Sub>> {
         let rows = self
             .rows(
@@ -1324,6 +1328,7 @@ impl Db {
     /// ponytail: every item of the feed for every subscriber, each time the feed is scanned with
     /// something new or a list changes. Fine at hundreds of items a feed; look only at new items
     /// on a scan if a feed with thousands makes scans slow.
+    #[tracing::instrument(skip_all)]
     pub async fn rehide(&self, feed_id: &str) -> Result<()> {
         let lists: Vec<(i64, Vec<String>)> = self
             .rows(
@@ -1730,6 +1735,7 @@ impl Db {
     /// read state for them. A Patreon creator read as one feed before it was split into shows
     /// owns every show's files, and `enclosures.url` is unique, so without this each show would
     /// list its items with nothing to play.
+    #[tracing::instrument(skip_all)]
     pub async fn adopt(&self, parent: &str, child: &str, listed: &[(&str, &str)]) -> Result<()> {
         use sea_orm::TransactionTrait;
         let holds = enclosures::Entity::find()
@@ -1773,6 +1779,7 @@ impl Db {
     /// A feed's enclosures skipped by one of its filters, by URL, with the reason: the verdicts a
     /// change of settings can overturn. A torrent held back while torrents are off is not a
     /// filter's call.
+    #[tracing::instrument(skip_all)]
     pub async fn skipped_by_filter(&self, feed_id: &str) -> Result<std::collections::HashMap<String, String>> {
         self.rows(
             "SELECT url, last_error FROM enclosures