Given a list of Account Ids, update each record's Rating based on its AnnualRevenue. Accounts with revenue ≥ 100,000,000 become Hot, revenue ≥ 20,000,000 become Warm, and all other or null values become Cold. Return the updated records and skip DML when the input list is empty.

Examples:

List<Id> accountIds = new List<Id>{ '001XXXXXXXXXXXXAAA', '001XXXXXXXXXXXXAAB' };
List<Account> updated = assignAccountPriority(accountIds);
// Results: Accounts are queried, their Rating is reassigned, and the updated records are returned