Support python wheel build (#787)

## Support Python wheel build

This PR modernizes the Python packaging for MSCCL++ by defining
dependencies and optional extras in `pyproject.toml`, enabling proper
wheel builds with `pip install ".[cuda12]"`.

### Changes

**`pyproject.toml`**
- Add `dependencies` (numpy, blake3, pybind11, sortedcontainers)
- Add `optional-dependencies` for platform-specific CuPy (`cuda11`,
`cuda12`, `cuda13`, `rocm6`), `benchmark`, and `test` extras
- Bump minimum Python version from 3.8 to 3.10

**`test/deploy/setup.sh`**
- Use `pip install ".[<platform>,benchmark,test]"` instead of separate
`pip install -r requirements_*.txt` + `pip install .` steps
- Add missing CUDA 13 case

**`docs/quickstart.md`**
- Update install instructions to use extras (e.g., `pip install
".[cuda12]"`)
- Document all available extras and clarify that `rocm6` builds CuPy
from source
- Update Python version references to 3.10

**`python/csrc/CMakeLists.txt`**, **`python/test/CMakeLists.txt`**
- Update `find_package(Python)` from 3.8 to 3.10

### Notes
- The `requirements_*.txt` files are kept for Docker base image builds
where only dependencies (not the project itself) should be installed.
- CuPy is intentionally not in base dependencies — users must specify a
platform extra to get the correct pre-built wheel (or source build for
ROCm).

---------

Co-authored-by: Claude Opus 4.6 <noreply@anthropic.com>
Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

python/test/CMakeLists.txt

@@ -1,7 +1,7 @@
 # Copyright (c) Microsoft Corporation.
 # Licensed under the MIT license.
 
-find_package(Python 3.8 COMPONENTS Interpreter Development.Module REQUIRED)
+find_package(Python 3.10 COMPONENTS Interpreter Development.Module REQUIRED)
 include(FetchContent)
 FetchContent_Declare(nanobind GIT_REPOSITORY https://github.com/wjakob/nanobind.git GIT_TAG v1.4.0)
 FetchContent_MakeAvailable(nanobind)