feat(dag-builder): add step fn

[glevco]

Motivation

Add ability to run a callback between propagations of the DAG builder.

Acceptance Criteria

• Add register_step_fn method to artifacts.

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	feat/step-fn-dag-builder
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	1.68 m (-2.32%) Baseline: 1.72 m	1.55 m (92.14%)	2.06 m (81.40%)

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[codecov]

Codecov Report

❌ Patch coverage is 50.00000% with 3 lines in your changes missing coverage. Please review.
✅ Project coverage is 86.31%. Comparing base (c78c142) to head (99a54c0).
⚠️ Report is 1 commits behind head on master.

Files with missing lines	Patch %	Lines
hathor/dag_builder/artifacts.py	50.00%	2 Missing and 1 partial ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #1555      +/-   ##
==========================================
+ Coverage   86.29%   86.31%   +0.01%     
==========================================
  Files         437      437              
  Lines       33605    33610       +5     
  Branches     5247     5248       +1     
==========================================
+ Hits        29000    29009       +9     
+ Misses       3597     3596       -1     
+ Partials     1008     1005       -3     

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