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/Dump/01_V2GMSG-SDP_Request.txt

@@ -0,0 +1,5 @@
+0000   33 33 00 00 00 01 10 22 33 44 55 66 86 dd 60 00   33....."3DUf..`.
+0010   00 00 00 12 11 ff fe 80 00 00 00 00 00 00 12 22   ..............."
+0020   33 ff fe 44 55 66 ff 02 00 00 00 00 00 00 00 00   3..DUf..........
+0030   00 00 00 00 00 01 c3 51 3b 0e 00 12 c8 18 01 fe   .......Q;.......
+0040   90 00 00 00 00 02 10 00                           ........