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/02_V2GMSG-SDP_Response.txt

@@ -0,0 +1,6 @@
+0000   10 22 33 44 55 66 80 34 28 2e 23 dd 86 dd 60 00   ."3DUf.4(.#...`.
+0010   00 00 00 24 11 ff fe 80 00 00 00 00 00 00 82 34   ...$...........4
+0020   28 ff fe 2e 23 dd fe 80 00 00 00 00 00 00 12 22   (...#.........."
+0030   33 ff fe 44 55 66 3b 0e c3 51 00 24 5e 42 01 fe   3..DUf;..Q.$^B..
+0040   90 01 00 00 00 14 fe 80 00 00 00 00 00 00 82 34   ...............4
+0050   28 ff fe 2e 23 dd d1 21 10 00                     (...#..!..