op-batcher: more robust detection of not-ready syncStatus

[geoknee]

This is a more robust way of detecting an invalid or "not yet ready" sync status. A valid status may have a 0 L2 safe block number, but the block hash would be the genesis block and therefore nonzero.

This should also allow us to safely run the batcher with --prefer-local-safe-l2=true even before we have fully resolved #14576

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 0.00%. Comparing base (6a8b234) to head (65e7726).
Report is 8 commits behind head on develop.

Additional details and impacted files

@@             Coverage Diff              @@
##           develop   #16298       +/-   ##
============================================
- Coverage    46.62%        0   -46.63%     
============================================
  Files         1368        0     -1368     
  Lines       110835        0   -110835     
============================================
- Hits         51675        0    -51675     
+ Misses       55514        0    -55514     
+ Partials      3646        0     -3646     

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