add core migration measuring and anti-bias to drmemtrace scheduler

[derekbruening]

Today the drmemtrace scheduler is not preferring to keep an input on the same core it last ran on. This issue covers measuring the migration statistics and probably adding some kind of bias to avoid migrations.

[derekbruening]

The plan is to implement separate runqueues per output. While testing the separate runqueue implementation I have found and fixed several bugs that affect the old global runqueue scheme as well. I'm going to include them as sub-parts of this issue:

• Direct switch migrations were not being added to the migration stat counter
• Direct switches were not setting blocked_start_time, resulting in too-short timeouts
• Quantum time left was underflowing in certain conditions where preempt and voluntary switch triggers coincided

Testing the separate runqueues has led to a number of other changes I'd like to make:

• Add a single simulator time scale option and have all the other options not be unitless (forcing the simulator to set every single one) but instead in simulated microsconds; apply to the existing quantum duration and block time max and possibly scale
• Exiting early: xref #6959 but not just when all are unscheduled
• Retry using a counter instead of wall-clock time for instr quanta to reduce nondeterminism and make analyzers behavior more like simulators, simplifying testing

[derekbruening]

The scheduler was refactored to use per-core runqueues. Closing this.