fix: making tests reproducible

[Becheler]

Before submitting

• This PR targets the develop branch.
• I searched for an existing PR or issue covering the same change.
• My contribution is licensed under the Boost Software License 1.0.

Type of change

• Bug fix
• New feature or API addition
• Refactor (no behavior change)
• Documentation
• Build, CI, or tooling
• Other (specify below)

Does this PR introduce a breaking change?

• Yes (describe migration impact below)
• No

What this PR does

Because code coverage reports varied stochastically, I had a look to tests determinism. I ended up seeding all random sources to 42.

Motivation

Testing

Checklist

• Existing tests pass (b2 in the test/ directory).
• New behavior is covered by a test, or this is a docs / build / refactor change.
• Documentation was updated if user-facing behavior changed.
• No new compiler warnings on the platforms I built against.

[github-actions]

Boost dependency footprint vs develop (auto-generated).
PR run 31381500277 vs develop run 31207793080 (bc05361cfd).

Header-inclusion weights (graph files pulling each direct dependency in):

No header-inclusion-weight changes.

Transitive Boost modules: 68 → 68 (0)

[github-actions]

Compiler-warning counts vs develop (auto-generated).
PR run 31381500310 vs develop run 31207793516 (bc05361cfd).

Job	Baseline	After	Delta
macos (clang, 14)	0	681	+681
macos (clang, 17)	0	641	+641
macos (clang, 20)	0	641	+641
ubuntu (clang-19, 14)	0	681	+681
ubuntu (clang-19, 17)	0	641	+641
ubuntu (clang-19, 20)	0	641	+641
ubuntu (clang-19, 23)	0	641	+641
ubuntu (gcc-14, 14)	827	827	0
ubuntu (gcc-14, 17)	0	949	+949
ubuntu (gcc-14, 20)	0	949	+949
ubuntu (gcc-14, 23)	0	949	+949
windows_msvc_14_3 (msvc-14.3)	0	962	+962

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 88.22%. Comparing base (e8e3f01) to head (bc05361).
⚠️ Report is 1 commits behind head on develop.

Additional details and impacted files

@@             Coverage Diff             @@
##           develop     #554      +/-   ##
===========================================
- Coverage    92.45%   88.22%   -4.24%     
===========================================
  Files          392      392              
  Lines        28214    27412     -802     
  Branches      8008     7997      -11     
===========================================
- Hits         26086    24183    -1903     
+ Misses        2024     1881     -143     
- Partials       104     1348    +1244     

Files with missing lines	Coverage Δ
test/astar_search_test.cpp	94.64% <100.00%> (-0.42%)	⬇️
test/betweenness_centrality_test.cpp	91.36% <100.00%> (-3.18%)	⬇️
test/bfs.cpp	92.10% <100.00%> (-6.58%)	⬇️
test/biconnected_components_test.cpp	61.11% <100.00%> (-7.31%)	⬇️
test/boykov_kolmogorov_max_flow_test.cpp	92.88% <100.00%> (-1.94%)	⬇️
test/bron_kerbosch_all_cliques.cpp	94.44% <100.00%> (-5.56%)	⬇️
test/csr_graph_test.cpp	90.90% <100.00%> (-1.24%)	⬇️
test/dfs.cpp	93.54% <100.00%> (-4.84%)	⬇️
test/dijkstra_no_color_map_compare.cpp	91.89% <100.00%> (-2.98%)	⬇️
test/floyd_warshall_test.cpp	61.90% <100.00%> (-3.08%)	⬇️
... and 19 more

... and 263 files with indirect coverage changes

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