Pin to Python 3.13 (#688)

cuML devcontainers fail to solve with Python 3.14, because onnxruntime
isn't yet available. This reverts the Python version pin to 3.13 until
that is resolved.

Author: bdice

.devcontainer/cuda12.9-conda/devcontainer.json

@@ -15,6 +15,7 @@
     "--ulimit",
     "nofile=500000"
   ],
+  "containerEnv": {"PYTHON_VERSION": "3.13"},
   "hostRequirements": {"gpu": "optional"},
   "features": {
     "./features/src/cuda": {

.devcontainer/cuda13.0-conda/devcontainer.json

@@ -15,6 +15,7 @@
     "--ulimit",
     "nofile=500000"
   ],
+  "containerEnv": {"PYTHON_VERSION": "3.13"},
   "hostRequirements": {"gpu": "optional"},
   "features": {
     "./features/src/cuda": {

.devcontainer/cuda13.1-conda/devcontainer.json

@@ -15,6 +15,7 @@
     "--ulimit",
     "nofile=500000"
   ],
+  "containerEnv": {"PYTHON_VERSION": "3.13"},
   "hostRequirements": {"gpu": "optional"},
   "features": {
     "./features/src/cuda": {