refactor[cartesian]: Replace is_start_state= with is_start_block=…

… when buiding the SDFG for DaCe (#1709)

When building an SDFG for DaCe it is sometimes necessary to specify the
starting point of the graph. In the past, `is_start_state=` was used for
this. In never versions of Dace, `is_start_state` has been deprecated
and replaced with `is_start_block`. This PR replaces the two occurrences
in the `cartesian/` folder and removes warnings generated during test
runs. It looks like the `next/` folder has already been cleaned.

src/gt4py/cartesian/gtc/dace/expansion/sdfg_builder.py

@@ -323,7 +323,7 @@ def visit_NestedSDFG(
     ) -> dace.nodes.NestedSDFG:
         sdfg = dace.SDFG(node.label)
         inner_sdfg_ctx = StencilComputationSDFGBuilder.SDFGContext(
-            sdfg=sdfg, state=sdfg.add_state(is_start_state=True)
+            sdfg=sdfg, state=sdfg.add_state(is_start_block=True)
         )
         self.visit(
             node.field_decls,

src/gt4py/cartesian/gtc/dace/oir_to_dace.py

@@ -39,7 +39,7 @@ class SDFGContext:
 
         def __init__(self, stencil: oir.Stencil):
             self.sdfg = dace.SDFG(stencil.name)
-            self.last_state = self.sdfg.add_state(is_start_state=True)
+            self.last_state = self.sdfg.add_state(is_start_block=True)
             self.decls = {decl.name: decl for decl in stencil.params + stencil.declarations}
             self.block_extents = compute_horizontal_block_extents(stencil)