add dart examples

src/guide/buy_btc.md

@@ -51,7 +51,15 @@ try {
 <section>
 
 ```dart
-// TODO add docs
+try {
+    BuyBitcoinResponse buyBitcoinResponse = buyBitcoin(
+        reqData: BuyBitcoinRequest(provider: BuyBitcoinProvider.Moonpay,
+        ),
+    ); 
+} catch {
+    // Handle error
+}
+
 ```
 </section>
 

src/guide/payments.md

@@ -61,8 +61,12 @@ try {
 
 ```dart
 try {
-    ReceivePaymentRequestData requestData = ReceivePaymentRequestData(amountSats: 3000, description: "Invoice for 3000 sats");
-    ReceivePaymentResponse invoice = await receivePayment(reqData: requestData);
+    ReceivePaymentResponse invoice = await receivePayment(
+        reqData: ReceivePaymentRequestData(
+            amountSats: 3000, 
+            description: "Invoice for 3000 sats",
+            ),
+        );
 } catch (error) {
     // handle error
 }

src/guide/receive_onchain.md

@@ -69,11 +69,7 @@ try {
 
 ```dart
 try {
-    // Optional user-selected dynamic fees (see Connecting to LSP section for details)
-    OpeningFeeParams? openingFeeParams = null;
-    ReceiveOnchainRequest request = new ReceiveOnchainRequest(openingFeeParams);
-    
-    SwapInfo swapInfo = await receiveOnchain(request);
+    SwapInfo swapInfo = await receiveOnchain(ReceiveOnchainRequest());
 
     // Send your funds to the below bitcoin address
     String address = swapInfo.bitcoinAddress;

src/guide/send_onchain.md

@@ -66,7 +66,7 @@ try {
 try {
     ReverseSwapPairInfo currentFees = await fetchReverseSwapFees();
 
-    print(`Total estimated fees for reverse swap: ${currentFees.totalEstimatedFees}`);
+    print("Total estimated fees for reverse swap: ${currentFees.totalEstimatedFees}");
 } catch (error) {
     // handle error
 }
@@ -161,8 +161,8 @@ console.log(`Maximum amount, in sats: ${currentFees.max}`);
 <section>
 
 ```dart
-print(`Minimum amount, in sats: ${currentFees.min}`);
-print(`Maximum amount, in sats: ${currentFees.max}`);
+print("Minimum amount, in sats: ${currentFees.min}");
+print("Maximum amount, in sats: ${currentFees.max}");
 ```
 </section>
 
@@ -262,7 +262,7 @@ try {
 
 ```dart
 String destinationAddress = "bc1..";
-int amountSat = currentFees.min;
+int amountSat = <amount>;
 int satPerVbyte = <fee rate>
 try {
     ReverseSwapInfo reverseSwapInfo = await sendOnchain(