python: skeleton pybind11 bindings (issue #6 task #197)

Каркас Python-пакета `cuframes`:
- python/pyproject.toml — scikit-build-core конфиг
- python/CMakeLists.txt — pybind11 module через FetchContent
- python/src/_native.cpp — module entry, error таксономия,
  enum mirrors (PixelFormat, SubscriberMode), version
- python/cuframes/__init__.py — re-export публичного API
- python/tests/test_smoke.py — smoke tests без real subscribe
- python/README.md — статус + build instructions
- CMakeLists.txt — подключение python/ при BUILD_PYTHON_BINDINGS=ON

Реальный subscriber/frame wrapper в следующих коммитах
(tasks #198-#202).

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

python/pyproject.toml

@@ -0,0 +1,47 @@
+[build-system]
+requires = [
+    "scikit-build-core>=0.10",
+    "pybind11>=2.13",
+]
+build-backend = "scikit_build_core.build"
+
+[project]
+name = "cuframes"
+version = "0.4.0"
+description = "Python bindings for cuframes — zero-copy CUDA frame sharing"
+readme = "README.md"
+license = { text = "LGPL-2.1+" }
+requires-python = ">=3.10"
+authors = [{ name = "Evgeny Demchenko", email = "demchenkoev@gmail.com" }]
+keywords = ["cuda", "video", "ipc", "zero-copy"]
+classifiers = [
+    "Development Status :: 3 - Alpha",
+    "Intended Audience :: Developers",
+    "License :: OSI Approved :: GNU Lesser General Public License v2 or later (LGPLv2+)",
+    "Programming Language :: Python :: 3",
+    "Programming Language :: Python :: 3.10",
+    "Programming Language :: Python :: 3.11",
+    "Programming Language :: Python :: 3.12",
+    "Topic :: Multimedia :: Video",
+]
+
+[project.optional-dependencies]
+torch = ["torch>=2.4"]
+cupy = ["cupy-cuda12x>=13"]
+dev = ["pytest>=8", "ruff>=0.6"]
+
+[tool.scikit-build]
+cmake.version = ">=3.20"
+cmake.build-type = "Release"
+build-dir = "build/{wheel_tag}"
+wheel.packages = ["cuframes"]
+# Будем строить только Python модуль; libcuframes собирается отдельно
+# в основном CMake-проекте и линкуется как imported target.
+cmake.args = ["-DBUILD_PYTHON_BINDINGS=ON", "-DBUILD_EXAMPLES=OFF", "-DBUILD_TOOLS=OFF"]
+cmake.source-dir = ".."
+
+[tool.scikit-build.cmake.define]
+BUILD_PYTHON_BINDINGS = "ON"
+
+[tool.pytest.ini_options]
+testpaths = ["tests"]