Remove RValue from ParametersContext so I can re-use it for calculated values from math.

src/renderer/renderer.rs

@@ -668,7 +668,9 @@ impl<'a> DustRenderer<'a> {
                     Some(_) => {
                         // TODO: math with body, calculate the value and use it like a select block
                         // Calculate the value
+                        let calculated_value = self.perform_math_operation(breadcrumbs, &param_map);
                         // Generate a ParametersContext with the result of the math operation as key
+
                         // calculate are_any_checks_true
                         // Generate a SelectContext
                         // render_maybe_body