Scheduler Fixture

This fixture is for manual testing purposes, and the patterns used in implementing it should not be used as a model. This is mainly for anyone working on making changes to the `schedule` module.

Tests:

1. Run Test 1

   Calls the callback within the frame when not blocked:

   Expected:
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   If you see the same above and below it's correct.

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   Actual:

2. Accepts multiple callbacks and calls within frame when not blocked

   Run Test 2
   Expected:
   -------------------------------------------------
   If you see the same above and below it's correct.

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   Actual:

3. Schedules callbacks in correct order when they use scheduleCallback to schedule themselves

   Run Test 3
   Expected:
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   If you see the same above and below it's correct.

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   Actual:

4. Calls timed out callbacks and then any more pending callbacks, defers others if time runs out

   Run Test 4
   Expected:
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   If you see the same above and below it's correct.

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   Actual:

5. When some callbacks throw errors, still calls them all within the same frame

   IMPORTANT: Open the console when you run this! Inspect the logs there!

   Run Test 5

6. When some callbacks throw errors and some also time out, still calls them all within the same frame

   IMPORTANT: Open the console when you run this! Inspect the logs there!

   Run Test 6

7. Continues calling callbacks even when user switches away from this tab

   Run Test 7
   Click the button above, observe the counter, then switch to another tab and switch back:
   If the counter advanced while you were away from this tab, it's correct.

8. Can pause execution, dump scheduled callbacks, and continue where it left off

   Run Test 8
   Click the button above, press "continue" to finish the test after it pauses:
   continue
   Expected:
   -------------------------------------------------
   If the test didn't progress until you hit "continue" and
   you see the same above and below afterwards it's correct.

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   Actual: