Refactor `loadMessage` function in room resource. #11732

Job	Run time
Check which packages changed	0s
AI bot Tests	44s
Boxel Motion Tests	1m 4s
Boxel Icons ensure raw icon changes only	1m 15s
Boxel UI ensure raw icon changes only	41s
Boxel UI Tests	3m 28s
Realm Server Tests (auth-client-test.ts)	5m 7s
Realm Server Tests (billing-test.ts)	5m 6s
Realm Server Tests (indexing-test.ts)	5m 50s
Realm Server Tests (index-query-engine-test.ts)	5m 25s
Realm Server Tests (index-writer-test.ts)	5m 15s
Realm Server Tests (loader-test.ts)	5m 26s
Realm Server Tests (module-syntax-test.ts)	5m 16s
Realm Server Tests (queue-test.ts)	5m 26s
Realm Server Tests (realm-server-test.ts)	6m 3s
Realm Server Tests (virtual-network-test.ts)	5m 7s
Boxel Tools VS Code Extension package	2m 20s
Matrix Client Tests (1, 12)	6m 2s
Matrix Client Tests (10, 12)	6m 2s
Matrix Client Tests (11, 12)	6m 4s
Matrix Client Tests (12, 12)	6m 3s
Matrix Client Tests (2, 12)	6m 3s
Matrix Client Tests (3, 12)	5m 15s
Matrix Client Tests (4, 12)	5m 21s
Matrix Client Tests (5, 12)	4m 58s
Matrix Client Tests (6, 12)	4m 43s
Matrix Client Tests (7, 12)	4m 22s
Matrix Client Tests (8, 12)	4m 19s
Matrix Client Tests (9, 12)	4m 18s
Deploy boxel to staging	0s
Merge Matrix reports and publish	31s
	2h 7m 34s

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