fix: actually tests finish_edge must fire once per edge

[Becheler]

An old test file testing an old bug does not assert anything. Now solved, and the file has been folded into dfs.cpp

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
• [ x] Build, CI, or tooling
• Other (specify below)

Does this PR introduce a breaking change?

• Yes (describe migration impact below)
• No

What this PR does

• Folded finish_edge_bug.cpp into dfs.cpp as test_finish_edge_is_called()
• deleted the file and its Jamfile entry

Motivation

Flickering CI coverage. Tests should not output only.

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 31402040385 vs develop run 31385980713 (0499661dda).

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

No header-inclusion-weight changes.

Transitive Boost modules: 68 → 68 (0)

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 92.82%. Comparing base (bc05361) to head (0499661).
⚠️ Report is 1 commits behind head on develop.

Additional details and impacted files

@@             Coverage Diff             @@
##           develop     #559      +/-   ##
===========================================
+ Coverage    88.22%   92.82%   +4.60%     
===========================================
  Files          392      391       -1     
  Lines        27412    28173     +761     
  Branches      7997     7996       -1     
===========================================
+ Hits         24183    26151    +1968     
- Misses        1881     1917      +36     
+ Partials      1348      105    -1243     

Files with missing lines	Coverage Δ
test/dfs.cpp	98.71% <100.00%> (+5.16%)	⬆️

... and 287 files with indirect coverage changes

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[github-actions]

Compiler-warning counts vs develop (auto-generated).
PR run 31402040412 vs develop run 31385980794 (0499661dda).

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