Consolidate binary relation arity checks

[jwalin-shah]

Summary

• route query/prove binary-arity enforcement through a named shared execution helper
• remove the unused duplicate HTTP command wrapper
• cover HTTP prove arity errors alongside query arity errors
• preserve Program.query arity error compatibility for existing callers/tests

Validation

• python3 -m pytest -q
• git diff --check

Residual risk

• Low: this keeps outward error text stable, but adapters still intentionally expose binary-only query/prove paths while Program relations remain variadic internally.

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