fix: satisfy clippy 1.97 lints failing on CI

- sanitize_current_ratio: and_then if/else -> filter
- screener/graph sorts: sort_by with reversed cmp -> sort_by_key(Reverse)
- insert_ksei_holdings_rows: manual Result match -> ?

Fixes the Clippy step on ubuntu-latest (rust 1.97) that the nix
toolchain (1.93.1) did not flag.

src/ownership/db.rs

@@ -196,10 +196,7 @@ fn insert_ksei_holdings_rows(
             )
             .map_err(|e| IdxError::DatabaseError(e.to_string()));
 
-        match changed {
-            Ok(n) => inserted += n,
-            Err(err) => return Err(err),
-        }
+        inserted += changed?;
     }
 
     Ok(inserted)