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/interfaces/errors.rs

@@ -98,11 +98,7 @@ impl AppError {
 
     /// Create a 413 Payload Too Large error.
     pub fn payload_too_large(message: impl Into<String>) -> Self {
-        Self::new(
-            StatusCode::PAYLOAD_TOO_LARGE,
-            message,
-            "PayloadTooLarge",
-        )
+        Self::new(StatusCode::PAYLOAD_TOO_LARGE, message, "PayloadTooLarge")
     }
 }