Add fake price fetcher for debug mode

SatsPrice/Network/FakePriceFetcher.swift

@@ -0,0 +1,18 @@
+//
+//  FakePriceFetcher.swift
+//  SatsPrice
+//
+//  Created by Terry Yiu on 2/21/24.
+//
+
+#if DEBUG
+import Foundation
+import BigDecimal
+
+/// Fake price fetcher that returns a randomized price. Useful for development testing without requiring a network call.
+class FakePriceFetcher: PriceFetcher {
+    func btcToUsd() async throws -> BigDecimal? {
+        BigDecimal(Double.random(in: 10000...100000))
+    }
+}
+#endif