refactor(model, cache): a full message object for `MessageUpdate` eve… #2491

Job	Run time
Spelling	8s
Format	14s
Minimum supported Rust version	51s
Test	1m 56s
Clippy	1m 0s
Build docs	1m 6s
Minimal crate versions	39s
Feature combinations	20m 30s
	26m 24s

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