breaking-change: Re-use graph traversal in bfs_shortest_path

[bobluppes]

This PR does the following:

• Adds an optional search_termination_strategy to BFS and DFS
• Refactors bfs_shortest_path to make use of the existing breadth_first_traverse
• Fixes the expected path length in shortest path tests

[codecov]

Codecov Report

Patch coverage: 99.20% and project coverage change: -0.08% ⚠️

Comparison is base (b4f9e10) 99.81% compared to head (275f359) 99.73%.

Additional details and impacted files

@@            Coverage Diff             @@
##             main      #65      +/-   ##
==========================================
- Coverage   99.81%   99.73%   -0.08%     
==========================================
  Files          22       23       +1     
  Lines        1076     1140      +64     
==========================================
+ Hits         1074     1137      +63     
- Misses          2        3       +1     

Files Changed	Coverage Δ
include/graaflib/algorithm/graph_traversal.tpp	96.55% <94.11%> (-3.45%)	⬇️
include/graaflib/algorithm/graph_traversal.h	100.00% <100.00%> (ø)
include/graaflib/algorithm/shortest_path.tpp	100.00% <100.00%> (ø)
test/graaflib/algorithm/graph_traversal_test.cpp	100.00% <100.00%> (ø)
test/graaflib/algorithm/shortest_path_test.cpp	100.00% <100.00%> (ø)

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