Clean up TaskQueueSuite

[dnr]

What changed?

• Split classic/new matcher at top level
• Use more pollers in most tests
• Use combined worker instead of separate
• Calculate observed rate with linear regression
• Refactor some tests
• Use testvars more
• Find fairness keys directly

Why?

Make test more reliable

How did you test it?

• [x] built
• [x] run locally and tested manually