refactor: migrate to tonutils v2, pytest, pyproject.toml

- tonutils 2.0.0: TonapiClient → ToncenterV3Client, wallet.transfer()
- classes → plain async functions across all utils and methods
- core/: constants.py, cookies.py, exceptions.py extracted
- DEVICE constant in constants.py (single source of truth)
- account/device serialised with json.dumps() in all tx payloads
- tests: unittest → pytest, conftest.py fixtures, 001/002 naming
- pyproject.toml: pytest + ruff config
- min balance check: 0.056 TON

pyproject.toml

@@ -0,0 +1,17 @@
+[tool.pytest.ini_options]
+testpaths    = ["tests"]
+python_files = ["[0-9][0-9][0-9]_test_*.py"]
+asyncio_mode = "auto"
+addopts      = "-v --tb=short"
+
+[tool.ruff]
+target-version = "py312"
+line-length    = 100
+src            = ["app", "tests"]
+
+[tool.ruff.lint]
+select = ["E", "W", "F", "I", "UP", "B", "C4", "RUF"]
+ignore = ["E501"]
+
+[tool.ruff.lint.isort]
+known-first-party = ["app"]