feat: make nakamoto mode the default

[obycode]

This enables nakamoto for xenon and mainnet modes, not just for "nakamoto-neon".

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 77.62%. Comparing base (d2649ff) to head (c96cb17).
Report is 24 commits behind head on next.

Additional details and impacted files

@@            Coverage Diff             @@
##             next    #4577      +/-   ##
==========================================
- Coverage   83.31%   77.62%   -5.69%     
==========================================
  Files         456      456              
  Lines      330593   331024     +431     
  Branches      323      317       -6     
==========================================
- Hits       275423   256973   -18450     
- Misses      55162    74043   +18881     
  Partials        8        8              

Files	Coverage Δ
testnet/stacks-node/src/config.rs	59.07% <100.00%> (-6.95%)	⬇️
testnet/stacks-node/src/main.rs	0.26% <ø> (+<0.01%)	⬆️

... and 172 files with indirect coverage changes

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