Ternary Expressions, Improved Integer Divisions, and Iteration Space Fix

Ternary expressions

This MR introduces ast nodes, typification, constant folding, and printing of ternary a ? b : c expressions. On top of that, freezing support for sympy.Piecewise is introduced.

Integer Division Improvements

This MR introduces the PsRem expression node for the C % operator, and adds constant folding for C-style integer division and remainder operations.

Fix: Iteration Space work items

Using the above, this MR fixes the computation of the amount of work items in an interation space if start, stop and step don't align.

src/pystencils/backend/ast/expressions.py

@@ -757,36 +757,3 @@ class PsArrayInitList(PsExpression):
 
     def __repr__(self) -> str:
         return f"PsArrayInitList({repr(self._items)})"
-
-
-def evaluate_expression(
-    expr: PsExpression, valuation: dict[str | PsSymbol, Any]
-) -> Any:
-    """Evaluate a pystencils backend expression tree with values assigned to symbols according to the given valuation.
-
-    Only a subset of expression nodes can be processed by this evaluator.
-    """
-
-    def visit(node):
-        match node:
-            case PsSymbolExpr(symb):
-                if value := valuation.get(symb, None) is not None:
-                    return value
-                else:
-                    return valuation[symb.name]
-
-            case PsConstantExpr(c):
-                return c.value
-
-            case PsUnOp(op1) if node.python_operator is not None:
-                return node.python_operator(visit(op1))
-
-            case PsBinOp(op1, op2) if node.python_operator is not None:
-                return node.python_operator(visit(op1), visit(op2))
-
-            case other:
-                raise NotImplementedError(
-                    f"Unable to evaluate {other}: No implementation available."
-                )
-
-    return visit(expr)