feat: Completes hvac-system-performance views and api call.

Sources/ViewController/Extensions/String+double.swift

@@ -8,7 +8,10 @@ private let numberFormatter: NumberFormatter = {
 }()
 
 extension String.StringInterpolation {
-  mutating func appendInterpolation(double: Double) {
+  mutating func appendInterpolation(double: Double, fractionDigits: Int = 2) {
+    let formatter = NumberFormatter()
+    formatter.numberStyle = .decimal
+    formatter.maximumFractionDigits = fractionDigits
     appendInterpolation(numberFormatter.string(from: NSNumber(value: double))!)
   }
 }