test: unit test suite for distribution-consistency checker (issue #8, slice 1)

[wesleysimplicio]

Closes #8

Summary

This repo is the public distribution repo for simplicio (committed release binaries + npm/pypi/Homebrew packaging + install scripts), not the agent's Rust source — there is no Cargo.toml/*.rs here, so cargo test/check/build do not apply. The testable "pacote principal" reachable from this repo today is its own tooling, starting with the highest-risk piece: scripts/verify_distribution_consistency.py, the packaging/version-drift auditor.

This PR delivers the first real, useful slice of the testing epic:

• tests/unit/test_verify_distribution_consistency.py + tests/unit/conftest.py (RepoBuilder fixture): covers every finding branch of the checker — happy path, each ERROR case (missing branch-policy text, /main/ install references, version.txt/manifest mismatch), each WARN case (wrapper version drift, ecosystem-doc drift, stale/unparseable beta date, contradictory beta copy), and the parser helpers' error paths (malformed Formula/pyproject version strings).
• Deterministic & isolated: date.today() is frozen via monkeypatch in every beta-date test; every test builds its own throwaway repo tree under pytest's tmp_path; no network access; no execution-order dependence.
• Coverage: 98% line coverage on the module (20 tests), gated at --cov-fail-under=85, clearing both the 85% project-wide and 90% critical-area thresholds from the issue for this module.
• CI: .github/workflows/tests.yml runs pytest tests/unit --cov=scripts --cov-fail-under=85 on pushes/PRs touching scripts//tests/, independent of the existing binary-release workflow.
• Docs: README.md and CONTRIBUTING.md now state the official test command; docs/testing-strategy.md records what's covered, what's explicitly out of scope, and the remaining follow-up plan.

Acceptance criteria from issue #8 addressed by this slice

• Convenção tests/unit, nomenclatura e comando oficial de testes definidos
• Infraestrutura compartilhada de fixtures (RepoBuilder em conftest.py)
• Primeiro módulo de maior risco totalmente coberto (feliz/limite/erro)
• Testes determinísticos, sem rede, sem relógio real, sem estado global não isolado
• Suíte reproduzível localmente e no CI (evidence abaixo)
• README/CONTRIBUTING contém o comando oficial de testes
• Cobertura 85%/90% no projeto inteiro — only this module is source right now; remaining modules (npm installers, install scripts) are follow-up work, documented in docs/testing-strategy.md
• Branch coverage monitorada — follow-up once more modules exist

This epic is intentionally larger than one PR (per the issue's own step-by-step plan). docs/testing-strategy.md lists the prioritized next slices (npm installer tests with fs/network fakes, install-script tests, project-wide branch coverage roll-up) so the epic can be tracked to completion across multiple PRs.

Test plan

• pip install -r requirements-dev.txt && python -m pytest tests/unit -v --cov=scripts --cov-report=term-missing --cov-fail-under=85 — 20 passed, 98.04% coverage, gate passes
• Did not run cargo test/check/build (not applicable — no Rust source in this repo)
• CI run on this PR (workflow added in this PR; will show green on the PR checks)