feat(sdk): add Python SDK with QUIC and FFI transport backends

Implements quicproquo-py with two transport backends:
- Async QUIC transport via aioquic with v2 protobuf wire format
- Synchronous Rust FFI transport via CFFI wrapping libquicproquo_ffi

Includes manual protobuf encode/decode (no codegen), full RPC coverage
(auth, delivery, channels, users, keys, health), PyPI-ready packaging,
async echo bot and FFI demo examples, and 15 passing unit tests.

sdks/python/pyproject.toml

@@ -0,0 +1,55 @@
+[build-system]
+requires = ["setuptools>=68.0", "wheel"]
+build-backend = "setuptools.build_meta"
+
+[project]
+name = "quicproquo"
+version = "0.1.0"
+description = "Python SDK for quicproquo E2E encrypted messenger"
+readme = "README.md"
+license = "MIT"
+requires-python = ">=3.10"
+authors = [{ name = "quicproquo contributors" }]
+keywords = ["quicproquo", "e2e", "encrypted", "messaging", "quic"]
+classifiers = [
+    "Development Status :: 3 - Alpha",
+    "Intended Audience :: Developers",
+    "License :: OSI Approved :: MIT License",
+    "Programming Language :: Python :: 3",
+    "Programming Language :: Python :: 3.10",
+    "Programming Language :: Python :: 3.11",
+    "Programming Language :: Python :: 3.12",
+    "Programming Language :: Python :: 3.13",
+    "Topic :: Communications :: Chat",
+    "Topic :: Security :: Cryptography",
+    "Framework :: AsyncIO",
+]
+
+dependencies = [
+    "aioquic>=1.0.0",
+    "protobuf>=5.26.0",
+    "cffi>=1.16.0",
+]
+
+[project.optional-dependencies]
+dev = [
+    "pytest>=8.0",
+    "pytest-asyncio>=0.23",
+    "mypy>=1.8",
+    "ruff>=0.3",
+]
+
+[project.urls]
+Homepage = "https://github.com/nicholasgasior/quicproquo"
+Repository = "https://github.com/nicholasgasior/quicproquo"
+
+[tool.setuptools.packages.find]
+include = ["quicproquo*"]
+
+[tool.ruff]
+target-version = "py310"
+line-length = 99
+
+[tool.mypy]
+python_version = "3.10"
+strict = true