add py.typed marker for Python client v3.0.2

[mcharytoniuk]

Summary

• Add PEP 561 py.typed marker file so downstream type checkers recognize the package as typed
• Bump version to 3.0.2
• Fix 13 pre-existing mypy strict mode errors in test_types.py (StrEnum .value comparisons, isinstance checks for custom serializer outputs)
• Fix pre-existing ruff formatting across 9 files

Test plan

• mypy --strict passes (50 files, 0 errors)
• ruff check and ruff format --check pass
• pytest passes (99 passed, 11 skipped integration tests)
• py.typed confirmed present in built wheel

[Copilot]

Pull request overview

Adds PEP 561 typing support for the paddler-client Python package so downstream type checkers treat it as a typed distribution, while also cleaning up strict-typing issues in tests and applying consistent Ruff formatting.

Changes:

• Add paddler_client/py.typed marker file for PEP 561 compliance.
• Bump package version from 3.0.1 to 3.0.2.
• Fix mypy --strict issues and apply Ruff formatting updates across tests and client modules.

Reviewed changes

Copilot reviewed 10 out of 11 changed files in this pull request and generated no comments.

Show a summary per file

File	Description
paddler_client_python/pyproject.toml	Bumps package version to 3.0.2 (and already advertises typed status via classifier).
paddler_client_python/paddler_client/py.typed	Adds PEP 561 marker to make the published package recognized as typed.
paddler_client_python/tests/test_types.py	Adjusts assertions (e.g., .value, isinstance) to satisfy mypy strict typing; minor formatting cleanups.
paddler_client_python/tests/test_stream_ndjson.py	Ruff-formatting of JSON construction and string concatenation in NDJSON stream tests.
paddler_client_python/tests/test_inference_message.py	Ruff-formatting of nested dict literals and JSON string assembly in inference message parsing tests.
paddler_client_python/tests/test_client_inference.py	Ruff-formatting of JSON response fixtures and assertion formatting in client inference tests.
paddler_client_python/tests/conftest.py	Ruff-formatting of comprehensions and exception raising in async test helpers.
paddler_client_python/paddler_client/inference_socket_url.py	Ruff-formatting of urlunparse call layout.
paddler_client_python/paddler_client/inference_socket_pool.py	Ruff-formatting of connection list initialization.
paddler_client_python/paddler_client/inference_socket_connection.py	Ruff-formatting of type annotations and logging call formatting.
paddler_client_python/paddler_client/error.py	Ruff-formatting of error constructors.

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