test: random_matching_test.cpp modernized, made self-contained and assertive

[Becheler]

Code coverage is very unstable, I am fixing unit tests, and many are not asserting much and only printing to cout, which is never checked: failed test still show as PASS.

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

• test now fails the build, not just stdout
• self-contained: hardcoded n/m as constexpr, dropped argc/argv + usage message; removed args from Jamfile.
• standard RNG: just use bare std::mt19937.
• Modernized typedefs
• Trimmed comments to single-line

Motivation

Our coverage is not great, code coverage flickers in CI

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 31389595260 vs develop run 31385980713 (ca9a25ebe7).

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 31389595234 vs develop run 31385980794 (ca9a25ebe7).

Job	Baseline	After	Delta
macos (clang, 14)	681	680	-1
macos (clang, 17)	641	641	0
macos (clang, 20)	641	641	0
ubuntu (clang-19, 14)	681	680	-1
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

[codecov]

Codecov Report

❌ Patch coverage is 92.30769% with 1 line in your changes missing coverage. Please review.
✅ Project coverage is 92.82%. Comparing base (bc05361) to head (ca9a25e).
⚠️ Report is 1 commits behind head on develop.

Files with missing lines	Patch %	Lines
test/random_matching_test.cpp	92.30%	0 Missing and 1 partial ⚠️

Additional details and impacted files

@@             Coverage Diff             @@
##           develop     #555      +/-   ##
===========================================
+ Coverage    88.22%   92.82%   +4.60%     
===========================================
  Files          392      392              
  Lines        27412    28166     +754     
  Branches      7997     7994       -3     
===========================================
+ Hits         24183    26146    +1963     
- Misses        1881     1914      +33     
+ Partials      1348      106    -1242     

Files with missing lines	Coverage Δ
test/random_matching_test.cpp	69.38% <92.30%> (+19.38%)	⬆️

... and 288 files with indirect coverage changes

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