[Consensus Observer] Parallelize message processing logic. #68181

Job	Run time
file_change_determinator	13s
rust-doc-tests	0s
rust-unit-tests	0s
rust-consensus-only-smoke-test	0s
rust-consensus-only-unit-test	0s
rust-cargo-deny	1m 43s
rust-lints	3m 25s
general-lints	26s
rust-check-merge-base	1m 15s
rust-cryptohasher-domain-separation-check	0s
rust-smoke-tests	0s
rust-build-cached-packages	0s
rust-targeted-unit-tests	12m 11s
	19m 13s

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