Replace black/isort/flake8 with ruff, migrate to uv/pyproject.toml

[halfguru]

Motivation

Why ruff?

• Replaces 3 tools (black, isort, flake8) + their plugins with a single, fast Rust-based tool
• 10-100x faster than the Python-based tools it replaces
• Actively maintained with a large community and growing ecosystem

Why uv?

• Replaces Poetry + poetry.lock with a modern, fast Python package manager
• pyproject.toml is the modern standard (PEP 621), consolidates config into one file
• Deterministic installs with uv.lock

Companion PR for the HA integration: dvd-dev/hilo#927

Summary

• Replace black, isort, and flake8 with ruff (formatter + linter) via ruff-pre-commit in .pre-commit-config.yaml
• Migrate pyproject.toml from Poetry to PEP 621 metadata, replace poetry.lock with uv.lock
• Raise minimum Python version to 3.11
• Drop Node.js/npm/prettier entirely
• Update devcontainer, dependabot, and CI to use uv for dependency management
• Add pytest job to CI alongside pre-commit
• Add mock-based unit tests for core modules (64 tests covering DeviceAttribute, DeviceReading, HiloDevice, utilities, state management)

Removed files

• .flake8: migrated to pyproject.toml
• .prettierignore: no longer needed without prettier
• .yamllint: dead config, not used by any pre-commit hook
• .nvmrc: no longer needed without Node.js
• package.json, package-lock.json: no longer needed without Node.js
• poetry.lock: replaced by uv.lock
• requirements.txt, test-requirements.txt: replaced by [project.dependencies] in pyproject.toml
• .github/workflows/constraints.txt: no longer needed