`MastForest` serialization #4930

Job	Run time
Clippy	1m 18s
rustfmt	22s
no-std (stable, wasm32-unknown-unknown)	1m 32s
Check Rust stable on ubuntu with --all-targets --no-default-features	1m 12s
no-std (nightly, wasm32-unknown-unknown)	1m 39s
Test Rust nightly on windows-2022	0s
Check Rust stable on ubuntu with --all-targets	1m 12s
Test Rust stable on ubuntu with --profile test-release	10m 32s
Check Rust stable on ubuntu with --all-targets --all-features	1m 11s
Check Rust nightly on ubuntu with --all-targets --no-default-features	1m 13s
Check Rust nightly on ubuntu with --all-targets	1m 15s
Test Rust stable on ubuntu with --profile test-release --doc	5m 48s
Check Rust nightly on ubuntu with --all-targets --all-features	1m 17s
Test Rust nightly on ubuntu with --profile test-release	11m 2s
Test Rust nightly on ubuntu with --profile test-release --doc	6m 20s
	45m 53s

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