Renames solBgHashVerify thread

[brooksprumo]

Problem

I'm working towards unifying all bits of accounts verification to be consistently named something related to "verify accounts" (e.g. the function, the thread, the thread pool, the logs, and the metrics).

For this PR, the thread that is spun up to verify accounts in the background is currently named "solBgHashVerify". I'd like to rename it to be more consistent with "verify accounts".

Summary of Changes

Rename it.

[codecov-commenter]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 83.2%. Comparing base (dbb0c6d) to head (68bea0d).
⚠️ Report is 2604 commits behind head on master.

Additional details and impacted files

@@           Coverage Diff           @@
##           master    #7340   +/-   ##
=======================================
  Coverage    83.2%    83.2%           
=======================================
  Files         797      797           
  Lines      361115   361115           
=======================================
+ Hits       300698   300699    +1     
+ Misses      60417    60416    -1     

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