Fix and un-allow `clippy::return_self_not_must_use` lints #1901

Job	Run time
cargo check (aarch64-android)	26s
cargo clippy (windows-latest)	2m 42s
cargo check (msrv) (windows-latest)	1m 39s
cargo check (msrv) (wasm32)	45s
cargo clippy (macos-latest)	1m 10s
cargo check (msrv) (macos-latest)	45s
cargo clippy (wasm32)	1m 24s
cargo clippy (ubuntu-latest)	1m 29s
cargo check (msrv) (ubuntu-latest)	48s
cargo doc	31s
formatting	23s
Prime LFS Cache	8s
cargo test (wasm32)	24s
typos	4s
cargo test (windows-latest)	2m 9s
cargo test (macos-latest)	1m 47s
cargo test (ubuntu-latest)	4m 10s
	20m 44s

Provide feedback