Sync queue updates

[rtibbles]

Summary

• 1 place in the queue per user, don't duplicate
• Filter by active or recently active transfer sessions to see if a sync is in progress
• Make queue item expire time dynamic, so that items with a smaller keep_alive expire more quickly
• Adds tests for the above
• Resyncs regardless of whether the sync task failed or not
• Makes queue places user/instance specific.

Reviewer guidance

Do the tests do what they purport?
Does the code do what it ought?

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Testing checklist

• Contributor has fully tested the PR manually
• If there are any front-end changes, before/after screenshots are included
• Critical user journeys are covered by Gherkin stories
• Critical and brittle code paths are covered by unit tests

PR process

• PR has the correct target branch and milestone
• PR has 'needs review' or 'work-in-progress' label
• If PR is ready for review, a reviewer has been added. (Don't use 'Assignees')
• If this is an important user-facing change, PR or related issue has a 'changelog' label
• If this includes an internal dependency change, a link to the diff is provided

Reviewer checklist

• Automated test coverage is satisfactory
• PR is fully functional
• PR has been tested for accessibility regressions
• External dependency files were updated if necessary (yarn and pip)
• Documentation is updated
• Contributor is in AUTHORS.md

[jredrejo]

Code looks good and in my tests it works perfectly. The user who was waiting longer is the first to sync everytime

[jredrejo]

it looks perfect

[jredrejo]

have I ever said how much I hate adding sleep to the tests?... I know this is a bad windows behaviour so one more reason not-to-love that OS
btw, this discussion is related https://stackoverflow.com/questions/85451/pythons-time-clock-vs-time-time-accuracy

[rtibbles]

Yeah, I am not a huge fan, but it seems like the only way :/