chore: use Self where applicable

[AaronChen0]

This PR applies the clippy::use_self lint across the codebase using:

cargo clippy --features "full-extra local-flow-stat utility-url-outline" --allow-dirty --all --fix -- -W clippy::use_self

Motivation:

• Improves readability and maintainability by reducing redundancy in impl blocks.
• Makes the codebase more idiomatic, aligning with common Rust practices.
• Helps future-proof refactoring (e.g. type renaming).