feat: Improve Report API performance (#9476)

- Re-write the methods for clarity
- Remove the dependency on the ReportHelper class.
- Remove n+1 queries in the average metric time series data.

spec/factories/reporting_events.rb

@@ -2,6 +2,7 @@ FactoryBot.define do
   factory :reporting_event do
     name { 'MyString' }
     value { 1.5 }
+    value_in_business_hours { 1 }
     account_id { 1 }
     inbox_id { 1 }
     user_id { 1 }