fix: resolve all clippy warnings and enforce cargo fmt

- display_helpers: convert module doc-comments to regular comments,
  merge identical text/markdown + text/ branches
- search_service: replace needless range loops with slice-based pagination
- folder_repository, folder_db_repository: collapse nested if statements
- favorites_pg_repository: remove unnecessary borrow on generic arg
- file_blob_read_repository: collapse 6 nested if-let blocks
- file_blob_write_repository: collapse nested if for dedup ref decrement
- chunked_upload_service: use div_ceil(), collapse 2 nested if blocks
- folder_handler: collapse nested if-let for owner check
- webdav_handler: replace 7x io::Error::new(ErrorKind::Other, ..) with
  io::Error::other(..)
- cargo fmt applied to all files

Passes: cargo clippy --all-targets --all-features -- -D warnings

src/application/services/folder_service.rs

@@ -182,10 +182,7 @@ impl FolderUseCase for FolderService {
         Ok(FolderDto::from(folder))
     }
 
-    async fn list_subtree_folders(
-        &self,
-        folder_id: &str,
-    ) -> Result<Vec<FolderDto>, DomainError> {
+    async fn list_subtree_folders(&self, folder_id: &str) -> Result<Vec<FolderDto>, DomainError> {
         let folders = self.folder_storage.list_subtree_folders(folder_id).await?;
         Ok(folders.into_iter().map(FolderDto::from).collect())
     }