Fix typing of constants

This is an umbrella MR combining a few small changes:

• Fixes typing of constants. If a typed Constant inside of an untyped ConstantExpr was encountered, the typification used to fail (see new test).
• Strengthens test_typify_integer_binops now that arbitrary expressions can be deferred.
• Increases the information content of two error messages.
• Fixes a typo.

src/pystencils/backend/kernelcreation/typification.py

@@ -126,8 +126,15 @@ class TypeContext:
                         raise TypificationError(
                             f"Can't typify constant with non-numeric type {self._target_type}"
                         )
-                    c.apply_dtype(self._target_type)
-                
+                    if c.dtype is None:
+                        c.apply_dtype(self._target_type)
+                    elif deconstify(c.dtype) != self._target_type:
+                        raise TypificationError(
+                            f"Type mismatch at constant {c}: Constant type did not match the context's target type\n"
+                            f"  Constant type: {c.dtype}\n"
+                            f"    Target type: {self._target_type}"
+                        )
+
                 case PsSymbolExpr(symb):
                     symb.apply_dtype(self._target_type)