cuda.core: import graph submodule after extension modules to avoid circular load

Importing cuda.core.graph from the top of cuda/core/__init__.py triggers a
load of cuda.core.graph._graph_builder, which cimports cuda.core._stream and
other extensions. While cuda.core itself is still initializing, those
circular loads leave the graph submodules partially initialized when
`from ._graph_builder import *` runs in cuda/core/graph/__init__.py, and
Graph, GraphBuilder, GraphCompleteOptions, and GraphDebugPrintOptions
silently fail to surface on cuda.core.graph.

Defer `import cuda.core.graph` until after every cuda.core._* extension has
been loaded so the inner `from ._graph_builder import *` finds a fully
initialized module. The standalone `import` form (rather than
`from cuda.core import graph`) keeps it from being collapsed back into the
checkpoint/system/utils block by ruff's import sorter; an `# isort: split`
marker pins the placement.

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

Author: Andy-Jost

cuda_core/cuda/core/__init__.py

@@ -28,7 +28,7 @@ def _import_versioned_module():
 del _import_versioned_module
 
 
-from cuda.core import checkpoint, graph, system, utils
+from cuda.core import checkpoint, system, utils
 from cuda.core._context import Context, ContextOptions
 from cuda.core._device import Device
 from cuda.core._device_resources import (
@@ -66,3 +66,10 @@ def _import_versioned_module():
     StreamOptions,
 )
 from cuda.core._tensor_map import TensorMapDescriptor, TensorMapDescriptorOptions
+
+# isort: split
+# Must come after the cuda.core._* extension imports above: loading graph
+# earlier interacts badly with the merged-wheel __path__ rewrite and leaves
+# Graph/GraphBuilder/GraphCompleteOptions/GraphDebugPrintOptions missing from
+# cuda.core.graph.
+import cuda.core.graph