Add -out option for file output and fix stdin detection logic

- Add -out/-o option to save decode/encode output to files
- Encoded files are saved as binary, console still shows hex strings
- Decoded XML files are saved as text
- Fix stdin detection logic to prioritize command line arguments
- Add missing System.Collections.Generic import for List<string> usage
- File extension auto-processing now supports -out option
- Clean up data folder with renamed files (data0-3.dump/xml)

🤖 Generated with [Claude Code](https://claude.ai/code)

Co-Authored-By: Claude <noreply@anthropic.com>

Data/data2.xml

@@ -0,0 +1,22 @@
+<?xml version="1.0" encoding="UTF-8"?>
+<ns1:V2G_Message xmlns:ns1="urn:iso:15118:2:2013:MsgDef" xmlns:ns2="urn:iso:15118:2:2013:MsgHeader" xmlns:ns3="urn:iso:15118:2:2013:MsgBody" xmlns:ns4="urn:iso:15118:2:2013:MsgDataTypes">
+	<ns1:Header>
+		<ns2:SessionID>41424230303038313</ns2:SessionID>
+	</ns1:Header>
+	<ns1:Body>
+		<ns3:PreChargeRes>
+			<ns3:ResponseCode>OK</ns3:ResponseCode>
+			<ns3:DC_EVSEStatus>
+				<ns4:NotificationMaxDelay>0</ns4:NotificationMaxDelay>
+				<ns4:EVSENotification>None</ns4:EVSENotification>
+				<ns4:EVSEIsolationStatus>Valid</ns4:EVSEIsolationStatus>
+				<ns4:EVSEStatusCode>EVSE_Ready</ns4:EVSEStatusCode>
+			</ns3:DC_EVSEStatus>
+			<ns3:EVSEPresentVoltage>
+				<ns4:Multiplier>0</ns4:Multiplier>
+				<ns4:Unit>V</ns4:Unit>
+				<ns4:Value>394</ns4:Value>
+			</ns3:EVSEPresentVoltage>
+		</ns3:PreChargeRes>
+	</ns1:Body>
+</ns1:V2G_Message>