Test the A174903 pair-vs-partner trap from issue 356

[Chessing234]

Summary

• scripts/oeis_false_match_traps.py recomputes r(n) (pairs of divisors) vs A174903's partner count.
• Test: they agree for n<60 and split at n=60 (13 vs 9), the example in Four systematic false-match hazards when linking problems to the OEIS #356.
• CONTRIBUTING points at that script so the other three traps stay in view.

Test plan

• python tests/test_oeis_false_match_traps.py

[teorth]

See #407: that PR adds the same two files (scripts/oeis_false_match_traps.py, tests/test_oeis_false_match_traps.py), and its version of the script is a strict superset of this one — this PR's 94 lines are exactly its prefix, with a sigma section appended. The two are not ancestrally related, so they collide on both paths.

That makes #407 the natural one to keep, since it already contains this work. The one thing it lacks is the two-line CONTRIBUTING.md addition here, which is worth carrying over rather than dropping.

Suggest folding that note into #407 and closing this one — but happy to do it the other way round if you would rather land the traps incrementally.

[Chessing234]

closing in favor of #407, which already has these traps plus the sigma ones. carried the CONTRIBUTING.md note over there.