feat: add initial test framework

[SecondSkoll]

Moves to a manifest generated test framework, implements some low level fixes, and adjust some rules.

[Copilot]

Pull Request Overview

This PR introduces a data-driven test framework for Vale rules using pytest, replacing manual test files with automated testing infrastructure. The framework validates Vale linting rules against expected outcomes defined in a manifest.

Key changes:

• Implements pytest-based test infrastructure with fixtures and parametrized tests
• Adds initial test coverage for two rules (000-US-spellcheck and 500-Repeated-words)
• Updates Vale configuration to enable repeated words rule and add RST directive ignores

Reviewed Changes

Copilot reviewed 41 out of 42 changed files in this pull request and generated 4 comments.

Show a summary per file

File	Description
tests/conftest.py	Core pytest configuration providing fixtures for manifest loading, Vale execution, and result validation
tests/test_rules.py	Main test functions implementing data-driven rule validation
tests/data/manifest.yml	Test manifest defining expected behaviors for two initial rules
tests/requirements.txt	Python dependencies including pytest, pyyaml, and vale 3.13.0.0
.github/workflows/pytest.yml	GitHub Actions workflow to run tests on Python 3.10 and 3.12
vale.ini	Configuration updates: enables repeated words rule, adds RST directive token ignores
test/.md, test/.rst, test/*.html	Removal of legacy manual test files
styles/Canonical/*.yml	Rule refinements including scope changes and pattern updates
styles/config/vocabularies/Canonical/accept.txt	Added "LTS" to accepted vocabulary
getting-started.md	Documentation addition about conditionally ignoring rules

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[akcano]

LGTM!