Add PriceFetcher API to fetch prices of multiple currencies

Sources/SatsPrice/Network/ManualPriceFetcher.swift

@@ -12,9 +12,19 @@ import Foundation
 
 /// Fake price fetcher that returns a randomized price. Useful for development testing without requiring a network call.
 class ManualPriceFetcher: PriceFetcher {
-    var price: Decimal = Decimal(1)
+    var prices: [Locale.Currency: Decimal] = [:]
 
     func convertBTC(toCurrency currency: Locale.Currency) async throws -> Decimal? {
-        return price
+        prices[currency]
+    }
+
+    func convertBTC(toCurrencies currencies: [Locale.Currency]) async throws -> [Locale.Currency : Decimal] {
+        guard !currencies.isEmpty else {
+            return [:]
+        }
+
+        let filteredCurrencies = currencies.filter { prices.keys.contains($0) }
+        let priceValues = filteredCurrencies.map { prices[$0, default: Decimal(0)] }
+        return Dictionary(uniqueKeysWithValues: zip(filteredCurrencies, priceValues))
     }
 }