build(cuda_bindings): declare cuda-pathfinder as a host-dependency

pixi-build-python runs `pip install --no-build-isolation` against the pixi
host environment, which bypasses `[build-system] requires` in
`pyproject.toml`. As a result, building `cuda_bindings` from source via the
pixi path-dependency workflow failed because `cuda_pathfinder` was not
present at build time — it was only declared in `pyproject.toml`.

Declare `cuda-pathfinder` as a path host-dependency in `cuda_bindings/pixi.toml`
so pixi installs it into the host env before the no-isolation build runs.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

Author: cpcloud

cuda_bindings/pixi.toml

@@ -121,6 +121,7 @@ setuptools = ">=80"
 setuptools-scm = ">=8"
 cython = ">=3.2,<3.3"
 pyclibrary = ">=0.1.7"
+cuda-pathfinder = { path = "../cuda_pathfinder" }
 cuda-cudart-static = "*"
 cuda-nvrtc-dev = "*"
 cuda-profiler-api = "*"