Create Dart snippets and reference them

Co-Authored-By: ok300 <106775972+ok300@users.noreply.github.com>

snippets/dart_snippets/lib/send_onchain.dart

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+import 'package:breez_sdk/breez_sdk.dart';
+import 'package:breez_sdk/bridge_generated.dart';
+
+Future<ReverseSwapPairInfo> estimateCurrentFees() async {
+  // ANCHOR: estimate-current-reverse-swap-total-fees
+  ReverseSwapFeesRequest req = const ReverseSwapFeesRequest(sendAmountSat: 50000);
+  ReverseSwapPairInfo currentFees = await BreezSDK().fetchReverseSwapFees(req: req);
+  print("Total estimated fees for reverse swap: ${currentFees.totalEstimatedFees}");
+  // ANCHOR_END: estimate-current-reverse-swap-total-fees
+  return currentFees;
+}
+
+void listCurrentFees({required ReverseSwapPairInfo currentFees}) {
+  // ANCHOR: get-current-reverse-swap-min-max
+  print("Minimum amount, in sats: ${currentFees.min}");
+  print("Maximum amount, in sats: ${currentFees.max}");
+  // ANCHOR_END: get-current-reverse-swap-min-max
+}
+
+Future<SendOnchainResponse> startReverseSwap({
+  required int amountSat,
+  required String onchainRecipientAddress,
+  required String pairHash,
+  required int satPerVbyte,
+}) async {
+  // ANCHOR: start-reverse-swap
+  SendOnchainRequest req = SendOnchainRequest(
+    amountSat: amountSat,
+    onchainRecipientAddress: onchainRecipientAddress,
+    pairHash: pairHash,
+    satPerVbyte: satPerVbyte,
+  );
+  SendOnchainResponse resp = await BreezSDK().sendOnchain(req: req);
+  // ANCHOR_END: start-reverse-swap
+  return resp;
+}
+
+Future<List<ReverseSwapInfo>> checkReverseSwapStatus() async {
+  // ANCHOR: check-reverse-swaps-status
+  List<ReverseSwapInfo> inProgRevSwapList = await BreezSDK().inProgressReverseSwaps();
+  for (var inProgRevSwap in inProgRevSwapList) {
+    print("Reverse swap ${inProgRevSwap.id} in progress, status is ${inProgRevSwap.status.name}");
+  }
+  // ANCHOR_END: check-reverse-swaps-status
+  return inProgRevSwapList;
+}