feat(core/graph/vf2++): implement VF2++ algorithm

[jnooree]

Checklist

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• Add documentation

[codecov]

Codecov Report

Attention: Patch coverage is 97.91045% with 7 lines in your changes missing coverage. Please review.

Project coverage is 91.17%. Comparing base (737518e) to head (7811f4d).
Report is 28 commits behind head on main.

Files with missing lines	Patch %	Lines
include/nuri/core/graph_vf2pp.h	98.10%	6 Missing ⚠️
include/nuri/core/graph.h	94.73%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #432      +/-   ##
==========================================
+ Coverage   90.98%   91.17%   +0.18%     
==========================================
  Files          51       52       +1     
  Lines       12453    12777     +324     
==========================================
+ Hits        11330    11649     +319     
- Misses       1123     1128       +5     

Files with missing lines	Coverage Δ
include/nuri/eigen_config.h	100.00% <ø> (ø)
include/nuri/core/graph.h	95.73% <94.73%> (+0.15%)	⬆️
include/nuri/core/graph_vf2pp.h	98.10% <98.10%> (ø)