Add single-stream GritQL test fixture and test harness

[covingtron]

Motivation

• Capture the supplied SQLite as_sqlite example as the input fixture for the forthcoming single-stream GritQL rule so the rule can be exercised against a real-world example.
• Record an explicit (empty) after fixture to represent the requested expected output for the rule.
• Provide a reproducible way to run all GritQL pattern examples from pytest so patterns can be validated in CI.

Description

• Added the single-stream fixtures tests/fixtures/single-stream/before.py (the provided as_sqlite example) and tests/fixtures/single-stream/after.py (empty expected output).
• Added a Grit pattern and configuration under .grit/ with .grit/grit.yaml and .grit/patterns/inline_single_use_assignment.md to capture the inline single-use assignment rule.
• Introduced a pytest wrapper tests/test_patterns.py that invokes the native grit patterns test --verbose runner against a copy of .grit.
• Added project metadata, packaging helper, CI workflows, and development files (pyproject.toml, build_backend.py, requirements.txt, .github/workflows/act.yaml, .github/workflows/package.yaml, .gitignore, and .grit/.gitignore) to support running the GritQL tests and building wheels for the bundled Grit CLI.

Testing

• Ran python -m py_compile tests/fixtures/single-stream/before.py tests/fixtures/single-stream/after.py and it succeeded.
• Ran repository checks git diff --cached --check and git show --check --stat --oneline HEAD to validate there are no staged whitespace/errors and both checks completed without errors.
• The pytest-driven GritQL test runner (tests/test_patterns.py) is provided but was not executed in this environment; it expects an installed grit binary and will be invoked by CI or in a developer environment via pytest.

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Codex Task