chore: apply cargo fmt + clippy cleanup across crate

Silence forward-looking dead_code on unused DAO modules, annotate
individual placeholder items, rewrite tautological assert!(true/false)
in token tests as panic! arms, and pick up fmt drift.

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

src/data/mod.rs

@@ -191,6 +191,7 @@ pub struct ThumbnailRequest {
     #[allow(dead_code)] // Part of API contract, may be used in future
     pub(crate) format: Option<ThumbnailFormat>,
     #[serde(default)]
+    #[allow(dead_code)] // Part of API contract, may be used in future
     pub(crate) shape: Option<ThumbnailShape>,
     /// Optional library filter. Accepts a library id (e.g. "1") or name
     /// (e.g. "main"). When omitted, defaults to the primary library.
@@ -434,11 +435,8 @@ mod tests {
         );
 
         match err.unwrap_err().into_kind() {
-            ErrorKind::ExpiredSignature => assert!(true),
-            kind => {
-                println!("Unexpected error: {:?}", kind);
-                assert!(false)
-            }
+            ErrorKind::ExpiredSignature => {}
+            kind => panic!("Unexpected error: {:?}", kind),
         }
     }
 
@@ -447,11 +445,8 @@ mod tests {
         let err = Claims::from_str("uni-֍ՓՓՓՓՓՓՓՓՓՓՓՓՓՓՓ");
 
         match err.unwrap_err().into_kind() {
-            ErrorKind::InvalidToken => assert!(true),
-            kind => {
-                println!("Unexpected error: {:?}", kind);
-                assert!(false)
-            }
+            ErrorKind::InvalidToken => {}
+            kind => panic!("Unexpected error: {:?}", kind),
         }
     }