Add performance counters for threading subsystem

[hkaiser]

Add new performance counters:

• allowing to retrieve the "pending accesses" "pending misses" for every scheduler thread - 5765842
• split "stolen" performance counter into four counters (stolen from pending, stolen to pending, stolen from staged, stolen to staged) - 5765842
• that measure the % of time spent creating and cleaning up of thread objects (see d8ae232, 5c934c5 for related commits)
• Increase precision of idle rate counters from 0.1% to 0.01%. Change creation/cleanup counters to be percentages of idle-rate (see b5aff61 for a related commit)

[brycelelbach]

Done as per scheduler_cleanup. WRT the idle rate precision, I think the 0.01% precision should be sufficient, although we certainly could go higher. 0.0.1% precision gives us an instrument uncertainty of 0.005%, which is likely close to the variance.