refactor(traversal): make neighbors traversal explicitly required

[glevco]

Depends on #1519

Motivation

Current behavior for traversals is that it traverses all DAG neighbors, unless they're explicitly skipped. This is open for mistakes that allow traversals through the entire graph when we forget to skip. This PR changes this behavior by requiring explicitly addition of neighbors, too.

Acceptance Criteria

• Refactor traversals, requiring users to either explicitly add or skip neighbors, otherwise it'll error.
• Refactor all usages to reflect this new behavior, generally this means:
  • Every bare continue/return was implicitly adding neighbors, so now they're added explicitly.
  • Every end-of-loop must call add_neighbors.
  • Both skip and add methods don't have any arguments.

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/traversal-opt-in
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 (-2.87%) Baseline: 1.73 m	1.55 m (92.66%)	2.07 m (80.94%)

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[codecov]

Codecov Report

❌ Patch coverage is 88.00000% with 6 lines in your changes missing coverage. Please review.
✅ Project coverage is 86.28%. Comparing base (cafc16b) to head (f34c2de).
⚠️ Report is 1 commits behind head on master.

Files with missing lines	Patch %	Lines
hathor/transaction/storage/traversal.py	80.76%	3 Missing and 2 partials ⚠️
hathor/p2p/sync_v2/streamers.py	75.00%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #1522      +/-   ##
==========================================
+ Coverage   86.27%   86.28%   +0.01%     
==========================================
  Files         438      438              
  Lines       33736    33762      +26     
  Branches     5267     5269       +2     
==========================================
+ Hits        29107    29133      +26     
  Misses       3617     3617              
  Partials     1012     1012              

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