feat: Begins air handler measurement form

Sources/StaticPressureFeature/FocusableField.swift

@@ -0,0 +1,21 @@
+import Foundation
+
+public protocol FocusableField {
+  var next: Self? { get }
+}
+
+extension FocusableField where Self: CaseIterable, Self: Equatable {
+  
+  public var next: Self? {
+    
+    guard let index = Self.allCases.firstIndex(of: self)
+    else { return nil }
+    
+    let endIndex = Self.allCases.endIndex
+    let nextIndex = Self.allCases.index(after: index)
+    
+    guard nextIndex < endIndex else { return nil }
+    return Self.allCases[nextIndex]
+    
+  }
+}