pinakes-core: add error context to tag and collection writes; map serde_json errors to Serialization variant

pinakes-core: distinguish task panics from cancellations in import error
  handling
Signed-off-by: NotAShelf <raf@notashelf.dev>
Change-Id: Icf5686f34144630ebf1935c47b3979156a6a6964

crates/pinakes-core/src/storage/postgres.rs

@@ -4295,6 +4295,11 @@ impl StorageBackend for PostgresBackend {
     &self,
     metadata: &crate::model::BookMetadata,
   ) -> Result<()> {
+    if metadata.media_id.0.is_nil() {
+      return Err(PinakesError::Database(
+        "upsert_book_metadata: media_id must not be nil".to_string(),
+      ));
+    }
     let mut client = self
       .pool
       .get()