hls: cargo fmt + clippy::cloned_ref_to_slice_refs

Pure mechanical pass on the files this branch added/modified:
rustfmt reflow of a few long lines / chains, and the one
non-pre-existing clippy warning — replacing
`&[rel_path.clone()]` with `std::slice::from_ref(&rel_path)` in
`handlers::video::generate_video` to avoid the alloc + clone for a
single-element slice.

All 707 tests still pass.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

src/video/legacy_migration.rs

@@ -38,10 +38,7 @@ pub struct RetireStats {
 
 impl RetireStats {
     pub fn total_deleted(&self) -> usize {
-        self.deleted_playlists
-            + self.deleted_segments
-            + self.deleted_sentinels
-            + self.deleted_tmp
+        self.deleted_playlists + self.deleted_segments + self.deleted_sentinels + self.deleted_tmp
     }
 }