Use u32 for time unit (for now) as it's hashable

bare-metrics-gui/src/config.rs

@@ -7,11 +7,11 @@ pub struct DashboardConfig {
     pub graphs: Vec<GraphConfig>,
 }
 
-#[derive(Deserialize, Clone)]
+#[derive(Deserialize, Clone, Debug, Hash)]
 pub enum MetricTransform {
     Rate {
         // Divisor in seconds. Would usually expect to see 1 (/sec), 60 (/min) or 3600 (/hour).
-        time_unit: f32,
+        time_unit: u32,
     },
 }