change `Debug` format for fields #855

Job	Run time
rustfmt	15s
Clippy	18s
Check with --all-features	30s
no-std (stable, wasm32-unknown-unknown)	34s
Check with --no-default-features	28s
no-std (nightly, wasm32-unknown-unknown)	34s
Test Rust stable on ubuntu	1m 13s
Test Rust nightly on ubuntu	1m 12s
	5m 4s

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