PohRecorder - sharable tick heights

[apfitzge]

Problem

• Observing tick height requires locking poh
• For leader decision, we currently want to know how far from leader we are.
  • currently this means we lock poh recorder very often

Summary of Changes

• Make tick_height and leader_first_tick_height into Arc<AtomicU64> (flag for None)
• Wrap both in safe interfaces so that things external to PohRecorder cannot modify them

Fixes #

[apfitzge]

Thought about having the same struct as above, but the loading is different since this can be None (via u64::MAX flag).

Thought cleaner to just separate them, even though they are very similar. Will also make it a bit harder to confuse the two once the shared structs are cloned outside of PohRecorder.

[apfitzge]

This, with other recent changes, can allow us to make DecisionMaker lock-free.
It will also be used in scheduler-bindings to provide leader-status messages:

• how long until we become leader
• progress in leader slot

until alpenglow**.

[codecov-commenter]

Codecov Report

❌ Patch coverage is 93.42105% with 5 lines in your changes missing coverage. Please review.
✅ Project coverage is 83.2%. Comparing base (6e14749) to head (59ba4c8).
⚠️ Report is 31 commits behind head on master.

Additional details and impacted files

@@           Coverage Diff           @@
##           master    #7355   +/-   ##
=======================================
  Coverage    83.2%    83.2%           
=======================================
  Files         797      797           
  Lines      361115   361154   +39     
=======================================
+ Hits       300699   300760   +61     
+ Misses      60416    60394   -22     

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[apfitzge]

#7372 is a follow-up to this change.