`MastForest` serialization #4931

Job	Run time
rustfmt	19s
Clippy	1m 14s
no-std (stable, wasm32-unknown-unknown)	1m 36s
Check Rust stable on ubuntu with --all-targets --no-default-features	1m 19s
no-std (nightly, wasm32-unknown-unknown)	1m 31s
Check Rust stable on ubuntu with --all-targets	1m 12s
Test Rust nightly on windows-2022	0s
Test Rust stable on ubuntu with --profile test-release	10m 18s
Check Rust stable on ubuntu with --all-targets --all-features	1m 16s
Check Rust nightly on ubuntu with --all-targets --no-default-features	1m 13s
Test Rust stable on ubuntu with --profile test-release --doc	5m 44s
Check Rust nightly on ubuntu with --all-targets	1m 15s
Test Rust nightly on ubuntu with --profile test-release	11m 21s
Test Rust nightly on ubuntu with --profile test-release --doc	6m 33s
Check Rust nightly on ubuntu with --all-targets --all-features	1m 18s
	46m 9s

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