Refactor cuda-bindings setup.py to defer CUDA_HOME check to build time

Move all CUDA-dependent logic (header parsing, code generation,
cythonization) from setup.py into a custom PEP 517 build backend
(build_hooks.py). Metadata queries (uv lock, uv sync, pip install
--dry-run) no longer require CUDA_HOME or CUDA_PATH to be set.

This follows the same pattern already used by cuda_core/build_hooks.py:
- Metadata hooks delegate directly to setuptools
- build_wheel/build_editable defer to _build_cuda_bindings()
- setup.py becomes a thin shim for ext_modules + parallel build_ext

Closes #1635

Co-authored-by: Cursor <cursoragent@cursor.com>

Author: kkraus14