feat(optimistic_block): Introduce the optimistic block struct #9458

Job	Run time
Backward Compatibility	11m 34s
Cargo Nextest (Linux)	10m 12s
Cargo Nextest (Linux Nightly)	13m 39s
Cargo Fmt	23s
Protobuf Backward Compatibility	13s
Protocol Schema	13m 33s
Database Migration	12m 9s
Genesis Changes	10m 14s
Sanity Checks	6m 19s
Style	40s
Upgradability	12m 0s
Cargo Deny	31s
Cargo Audit	20s
Cargo Clippy	9m 5s
Non-default Configuration Builds	1m 17s
Themis	38s
Unused Dependencies	7m 5s
Rust Doctests	10m 57s
Cargo check publishable packages separately (Linux, linux, ubuntu-latest)	8m 10s
Cargo check publishable packages separately (Windows, win, windows-latest)	3m 8s
Upload Coverage	26s
Generate Coverage Artifact (unit, unit)	2m 58s
	2h 15m 31s

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