Micro optimizations on new-state-mgmt service for initial syncing

[terencechain]

Built on top of #5215

Micro optimizations on new state mgmt service to optimize initial syncing speed

• Batch save state summary
• A node shouldn't wastefully retrieve a finalized state just to get the finalized slot for migration, let's retrieve finalized block instead
• In the event of playback, instead of using epoch boundary state of slot N, use the last available state of slot N in the DB. It's more efficient

All these minor updates increase initial sync bps for new-state-mgmt by 30-40%

[codecov]

Codecov Report

Merging #5241 into master will decrease coverage by 0.35%.
The diff coverage is 73.72%.

@@            Coverage Diff             @@
##           master    #5241      +/-   ##
==========================================
- Coverage   56.06%   55.71%   -0.36%     
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  Files         291      291              
  Lines       23306    22866     -440     
==========================================
- Hits        13066    12739     -327     
+ Misses       8428     8348      -80     
+ Partials     1812     1779      -33