Cleanup and fix py-torch concretization

• small cleanup to avoid having to specify the compiler per "spec line"
  • introduce "packages" section in env file
  • also move python version constraint there…
• fix py-torch package (forks into local packages/ folder)
• fix py-torch concretization

packages/py-torch/cusparseGetErrorString.patch

+diff --git a/aten/src/ATen/native/sparse/cuda/SparseCUDABlas.cu b/aten/src/ATen/native/sparse/cuda/SparseCUDABlas.cu
+index 1cee04c200..f46003d9a9 100644
+--- a/aten/src/ATen/native/sparse/cuda/SparseCUDABlas.cu
++++ b/aten/src/ATen/native/sparse/cuda/SparseCUDABlas.cu
+@@ -10,48 +10,6 @@
+ namespace at { namespace native { namespace sparse { namespace cuda {
+ 
+ 
+-std::string cusparseGetErrorString(cusparseStatus_t status) {
+-  switch(status)
+-  {
+-    case CUSPARSE_STATUS_SUCCESS:
+-      return "success";
+-
+-    case CUSPARSE_STATUS_NOT_INITIALIZED:
+-      return "library not initialized";
+-
+-    case CUSPARSE_STATUS_ALLOC_FAILED:
+-      return "resource allocation failed";
+-
+-    case CUSPARSE_STATUS_INVALID_VALUE:
+-      return "an invalid numeric value was used as an argument";
+-
+-    case CUSPARSE_STATUS_ARCH_MISMATCH:
+-      return "an absent device architectural feature is required";
+-
+-    case CUSPARSE_STATUS_MAPPING_ERROR:
+-      return "an access to GPU memory space failed";
+-
+-    case CUSPARSE_STATUS_EXECUTION_FAILED:
+-      return "the GPU program failed to execute";
+-
+-    case CUSPARSE_STATUS_INTERNAL_ERROR:
+-      return "an internal operation failed";
+-
+-    case CUSPARSE_STATUS_MATRIX_TYPE_NOT_SUPPORTED:
+-      return "the matrix type is not supported by this function";
+-
+-    case CUSPARSE_STATUS_ZERO_PIVOT:
+-      return "an entry of the matrix is either structural zero or numerical zero (singular block)";
+-
+-    default:
+-      {
+-        std::ostringstream oss;
+-        oss << "unknown error " << static_cast<int64_t>(status);
+-        return oss.str();
+-      }
+-  }
+-}
+-
+ inline void CUSPARSE_CHECK(cusparseStatus_t status)
+ {
+   if (status != CUSPARSE_STATUS_SUCCESS) {