refactor(model, cache): a full message object for `MessageUpdate` event #2489

Job	Run time
Spelling	9s
Minimum supported Rust version	1m 6s
Format	18s
Clippy	1m 5s
Build docs	1m 5s
Feature combinations	20m 17s
Minimal crate versions	56s
Test	1m 53s
	26m 49s

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