Split the report output service under the file-length limit #4065

Problem

The file-length quality guard fails on master (e5de69ef7), so the "Quality guards" job fails on every open pull request:

[api.quality.file-length] file-length: policyengine_api/services/report_output_service.py has 805 lines, over the 800-line limit for source files.

#4044 grew report_output_service.py from 792 to 805 lines. #4054, which added the 800-line rule (#4052), then merged on a CI run from before #4044 merged: the branch rules don't require a pull request to be up to date with master, so neither pull request's CI saw both changes together.

Proposal

Split report_output_service.py by responsibility into modules under the limit, without changing behaviour or any import path, and without adding it to the rule's baseline. The tests that read the file's source should also read the new module.