TransactionScheduler: CLI and hookup for central-scheduler

[apfitzge]

Problem

Need a way to use the new BankingStage w/ central scheduler

Summary of Changes

• Factor out some code for spawning legacy/thread-local-multi-iterator banking stage threads
• Add BlockProductionMethod::CentralScheduler variant
• Add path to spawn new scheduling thread, workers, and legacy voting threads
• Re-use existing banking stage test to verify new production method works in basic fashion

Fixes #

[codecov]

Codecov Report

Merging #33890 (d3b37ce) into master (ba112a0) will increase coverage by 0.0%.
Report is 4 commits behind head on master.
The diff coverage is 98.2%.

@@           Coverage Diff            @@
##           master   #33890    +/-   ##
========================================
  Coverage    81.8%    81.9%            
========================================
  Files         810      810            
  Lines      218148   218247    +99     
========================================
+ Hits       178650   178814   +164     
+ Misses      39498    39433    -65     

[tao-stones]

lgtm