Rework dataclass array container arithmetic

- Deprecate automatic broadcasting of array context arrays
- Introduce Bcast as an object to represent broadcast rules
- Warn about uses of numpy array broadcasting, deprecated earlier
- Clarify documentation, warning wording

arraycontext/__init__.py

@@ -43,7 +43,15 @@
     register_multivector_as_array_container,
     serialize_container,
 )
-from .container.arithmetic import with_container_arithmetic
+from .container.arithmetic import (
+    Bcast,
+    Bcast1,
+    Bcast2,
+    Bcast3,
+    BcastNLevels,
+    BcastUntilActxArray,
+    with_container_arithmetic,
+)
 from .container.dataclass import dataclass_array_container
 from .container.traversal import (
     flat_size_and_dtype,
@@ -103,6 +111,12 @@
     "ArrayOrContainerOrScalarT",
     "ArrayOrContainerT",
     "ArrayT",
+    "Bcast",
+    "Bcast1",
+    "Bcast2",
+    "Bcast3",
+    "BcastNLevels",
+    "BcastUntilActxArray",
     "CommonSubexpressionTag",
     "EagerJAXArrayContext",
     "ElementwiseMapKernelTag",
@@ -151,7 +165,6 @@
     "unflatten",
     "with_array_context",
     "with_container_arithmetic",
-    "with_container_arithmetic"
 )