Fi 607 cache ref resolution

[arscan]

Fixes a few bugs in the US Core generator. Also caps resource resolution step to a max number of references to follow (currently set to 50), and won't resolve the same reference multiple times, because this was tying up our database and tests were taking way too long to run for little benefit.

Submitter:

• This pull request describes why these changes were made
• Internal ticket for this PR:
• Internal ticket links to this PR
• Internal ticket is properly labeled (Community/Program)
• Internal ticket has a justification for its Community/Program label
• Code diff has been reviewed for extraneous/missing code
• Tests are included and test edge cases
• Tests/code quality metrics have been run locally and pass

Reviewer 1:

Name:

• Code is maintainable and reusable, reuses existing code and infrastructure
  where appropriate, and accomplishes the task's purpose
• The tests appropriately test the new code, including edge cases
• You have tried to break the code

Reviewer 2:

Name:

• Code is maintainable and reusable, reuses existing code and infrastructure
  where appropriate, and accomplishes the task's purpose
• The tests appropriately test the new code, including edge cases
• You have tried to break the code

[okeefm]

Tested the generator and the modules it generates; looks good to me.