Add support for manual price entry

SatsPrice/Network/ManualPriceFetcher.swift

@@ -0,0 +1,18 @@
+//
+//  ManualPriceFetcher.swift
+//  SatsPrice
+//
+//  Created by Terry Yiu on 8/29/24.
+//
+
+import Foundation
+import BigDecimal
+
+/// Fake price fetcher that returns a randomized price. Useful for development testing without requiring a network call.
+class ManualPriceFetcher: PriceFetcher {
+    var price: BigDecimal = 1
+
+    func btcToUsd() async throws -> BigDecimal? {
+        return price
+    }
+}