qbft: move chain split check to preprepare round

[KaloyanTanev]

It's safer to do the chain split check in the pre-prepare round.

WIP: still testing

category: feature
ticket: none
feature_flag: chain_split_halt

[sonarqubecloud]

Quality Gate passed

Issues
0 New issues
0 Accepted issues

Measures
0 Security Hotspots
0.0% Coverage on New Code
0.0% Duplication on New Code

See analysis details on SonarQube Cloud

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 53.50%. Comparing base (1cb7223) to head (df69843).
⚠️ Report is 1 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #4011      +/-   ##
==========================================
+ Coverage   53.49%   53.50%   +0.01%     
==========================================
  Files         224      224              
  Lines       37353    37353              
==========================================
+ Hits        19982    19986       +4     
+ Misses      15254    15244      -10     
- Partials     2117     2123       +6     

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