Draft: Changes for compatibility with pystencils 2.0

Introduce a significant number of patches for compatibility with the upcoming pystencils 2.0.

Changes

Testing & CI

• Introduce nox to orchestrate environments and testing
• Adapt CI to use nox sessions where applicable
• Remove minimal_conda and ubuntu CI tasks
  • Since the pycodegen/ubuntu docker image is based on a CUDA image, and using a virtual environment for Python, the ubuntu task effectively does the same as the Nox+CUDA task
• Introduce nox session and CI task to test against pystencils/v2.0-dev

Status

• Fix field duplication in create_lb_update_rule: Remove the workaround once field duplication is fixed in pystencils
• Data types in boundary handling: LatticeBoltzmannBoundaryHandling does not allow to specify a data type and always uses float64. This leads to type errors when combined with LB fields with float32 dtype.
• Mixed precision: Need to explicitly insert casts at field reads/writes when computing and storing PDFs in different float formats

tests/advanced_streaming/test_advanced_streaming_noslip.py

@@ -43,7 +43,7 @@ def test_advanced_streaming_noslip_single_cell(stencil, streaming_pattern, prev_
     index_struct_dtype = numpy_data_type_for_boundary_object(noslip, stencil.D)
 
     index_field = Field('indexVector', FieldType.INDEXED, index_struct_dtype, layout=[0],
-                        shape=(TypedSymbol("indexVectorSize", np.int64), 1), strides=(1, 1))
+                        shape=(TypedSymbol("indexVectorSize", np.int32), 1), strides=(1, 1))
     index_vector = np.array([pos + (d,) for d in range(stencil.Q)], dtype=index_struct_dtype)
 
     ast = create_lattice_boltzmann_boundary_kernel(pdf_field,