`Composition`: Use `hashbrown::HashMap` #33

Job	Run time
cargo clippy (wasm32)	24s
cargo check (msrv) (windows-latest)	45s
cargo check (msrv) (wasm32)	22s
cargo check (msrv) (macos-latest)	35s
cargo clippy (windows-latest)	1m 14s
cargo check (msrv) (ubuntu-latest)	25s
cargo doc	22s
cargo clippy (macos-latest)	35s
cargo clippy (ubuntu-latest)	39s
formatting	42s
cargo test (wasm32)	19s
cargo test (windows-latest)	52s
typos	7s
cargo test (macos-latest)	35s
cargo test (ubuntu-latest)	18s
	8m 14s

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