feat: Adds furnace heating interpolations.

Sources/Models/FurnaceInterpolation.swift

@@ -0,0 +1,53 @@
+public enum FurnaceInterpolation {
+
+  public struct Request: Codable, Equatable, Sendable {
+
+    public let elevation: Int?
+    public let winterDesignTemperature: Int
+    public let heatLoss: Int
+    public let inputRating: Int
+    public let afue: Double
+
+    public init(
+      elevation: Int? = nil,
+      winterDesignTemperature: Int,
+      heatLoss: Int,
+      inputRating: Int,
+      afue: Double
+    ) {
+      self.elevation = elevation
+      self.winterDesignTemperature = winterDesignTemperature
+      self.heatLoss = heatLoss
+      self.inputRating = inputRating
+      self.afue = afue
+    }
+  }
+
+  public struct Response: Codable, Equatable, Sendable {
+
+    public let failed: Bool
+    public let failures: [String]?
+    public let altitudeAdjustmentMultiplier: Double?
+    public let capacityAsPercentOfLoad: Int
+    public let oversizingLimit: Int
+    public let undersizingLimit: Int
+    public let outputCapacity: Int
+
+    public init(
+      failures: [String]? = nil,
+      altitudeAdjustmentMultiplier: Double? = nil,
+      capacityAsPercentOfLoad: Int,
+      oversizingLimit: Int,
+      undersizingLimit: Int,
+      outputCapacity: Int
+    ) {
+      self.failed = failures == nil ? false : !failures!.isEmpty
+      self.failures = failures
+      self.altitudeAdjustmentMultiplier = altitudeAdjustmentMultiplier
+      self.capacityAsPercentOfLoad = capacityAsPercentOfLoad
+      self.oversizingLimit = oversizingLimit
+      self.undersizingLimit = undersizingLimit
+      self.outputCapacity = outputCapacity
+    }
+  }
+}