refactor(nano): Move the nano execution logic to a separate file

[msbrogli]

Motivation

This PR moves the nano execution logic from the Block Consensus Algorithm to a separate file. This is a preparation for upcoming features such as block execution replay and block execution logging.

Acceptance Criteria

1. Introduce NCBlockExecutor to encapsulate nano execution logic.
2. Move existing nano execution code from BlockConsensusAlgorithm into NCBlockExecutor.
3. Keep the feature activation logic in the BlockConsensusAlgorithm.
4. Keep all existing behavior intact; this is intended as a pure refactor.

Checklist

• If you are requesting a merge into master, confirm this code is production-ready and can be included in future releases as soon as it gets merged

[github-actions]

Bencher Report

Branch	refactor/nano-consensus-execution
Testbed	ubuntu-22.04

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Benchmark	Latency	Benchmark Result minutes (m) (Result Δ%)	Lower Boundary minutes (m) (Limit %)	Upper Boundary minutes (m) (Limit %)
sync-v2 (up to 20000 blocks)	📈 view plot 🚷 view threshold	1.69 m (-1.71%) Baseline: 1.72 m	1.55 m (91.56%)	2.06 m (81.91%)

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[codecov]

Codecov Report

❌ Patch coverage is 92.34694% with 15 lines in your changes missing coverage. Please review.
✅ Project coverage is 86.34%. Comparing base (73d3e56) to head (ccfe8c6).
⚠️ Report is 2 commits behind head on master.

Files with missing lines	Patch %	Lines
hathor/nanocontracts/execution/block_executor.py	91.80%	11 Missing and 4 partials ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #1535      +/-   ##
==========================================
+ Coverage   86.27%   86.34%   +0.07%     
==========================================
  Files         437      439       +2     
  Lines       33662    33690      +28     
  Branches     5269     5271       +2     
==========================================
+ Hits        29042    29091      +49     
+ Misses       3611     3596      -15     
+ Partials     1009     1003       -6     

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