[pixi] Add pixi support for running all sub-package tests (#1398)

* Adding a global metapackage level pixi.tom to run all the pytest suites with the same virtual environment

* Removing tasks

* precommit

* removing the conda environment detection support

* Using depends-on instead of coping the command line

* simplifying the task command line using bash parameter expansion

* improve doc comments

* refactor: no bash, and configurable arguments

* chore: consistency with -e/--environment flags

* refactor: remove features

* refactor: bring back envs for -e behavior

* refactor: use envars to set child environment

* refactor: add pixi dust

* refactor: more pixi dust

* refactor: remove envars

---------

Co-authored-by: Phillip Cloud <417981+cpcloud@users.noreply.github.com>

Author: rparolin

cuda_core/pixi.lock

@@ -0,0 +1,50 @@
+# SPDX-FileCopyrightText: Copyright (c) 2025 NVIDIA CORPORATION & AFFILIATES. All rights reserved.
+#
+# SPDX-License-Identifier: Apache-2.0
+
+[workspace]
+channels = ["conda-forge"]
+platforms = ["linux-64", "linux-aarch64", "win-64"]
+
+[feature.cu12.dependencies]
+[feature.cu13.dependencies]
+
+[environments]
+cu12 = { features = ["cu12"] }
+cu13 = { features = ["cu13"] }
+
+[activation.env]
+PIXI_ENVIRONMENT_NAME = "${PIXI_ENVIRONMENT_NAME/default/cu13}"
+
+# Test Tasks
+# Runs tests across all sub-packages: pathfinder → bindings → core (dependency order)
+# Each sub-package has its own pixi.toml; the -e environment propagates via PIXI_ENVIRONMENT_NAME
+#
+# Usage: pixi run test | pixi run -e cu12 test | pixi run -e cu13 test
+[target.linux.tasks.test-pathfinder]
+cmd = [
+    "pixi",
+    "run",
+    "--manifest-path",
+    "$PIXI_PROJECT_ROOT/cuda_pathfinder",
+    "test",
+]
+
+[target.linux.tasks.test-bindings]
+cmd = [
+    "pixi",
+    "run",
+    "--manifest-path",
+    "$PIXI_PROJECT_ROOT/cuda_bindings",
+    "test",
+]
+
+[target.linux.tasks.test-core]
+cmd = ["pixi", "run", "--manifest-path", "$PIXI_PROJECT_ROOT/cuda_core", "test"]
+
+[target.linux.tasks.test]
+depends-on = [
+    { task = "test-pathfinder" },
+    { task = "test-bindings" },
+    { task = "test-core" },
+]