fix: make Transform enum non-exhaustive (#194)

Author: sd2k

crates/augurs-forecaster/src/transforms.rs

@@ -44,6 +44,7 @@ impl Transforms {
 
 /// A transformation that can be applied to a time series.
 #[derive(Debug)]
+#[non_exhaustive]
 pub enum Transform {
     /// Linear interpolation.
     ///