Refactor `for_agent` / clear up API usage

[joepio]

Refactor `for_agent` / clear up API usage

[joepio]

I'm implementing the new ForAgent enum, and as I'm doing that, I'm trying to change some defaults. For example, I don't want Query::default to do powerful Sudo queries, but instead, default to Public queries.

Unfortunately, this broke one of the tests. db::test::destroy_resource_and_check_collection_and_commits Now fails, because it returns 2 instead of 1 Agents in one of the first steps. Turns out that the init command is actually fetching an agent from AtomicData.dev, probably during populate_collection, due to a rights check...

It turned out that because I set the Query::default to have ForAgent::public, it now actually performed rights checks, even during populate, which meant that when it tried to make the Class collections, it checked if public_agent had read rights for all of these Classes, which meant it had to check all parents, which for one Class (the Error class) was an actual agent. And THAT bumped the amount of Agents with one.