Draft: Changes for compatibility with pystencils 2.0

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

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/test_cpu_gpu_equivalence.py

@@ -16,6 +16,9 @@ def run_equivalence_test(domain_size, lbm_config, lbm_opt, base_config, time_ste
     cpu_scenario = create_channel(domain_size=domain_size, pressure_difference=0.001,
                                   lbm_config=lbm_config, lbm_optimisation=lbm_opt, config=config)
     config = replace(base_config, target=Target.GPU)
+    if not IS_PYSTENCILS_2:
+        from pystencils.enums import Backend
+        config = replace(config, backend=Backend.CUDA)
     gpu_scenario = create_channel(domain_size=domain_size, pressure_difference=0.001,
                                   lbm_config=lbm_config, lbm_optimisation=lbm_opt, config=config)