Add code style CI

[DaniusKalv]

Summary

• Add code-style.yml calling Kurokesu/ci kernel-code-style workflow
• Replace 561 line .clang-format inherited from gen-1 with the canonical 113 line one
• Fix checkpatch warnings: filename in both file headers, missing blank line after a declaration, braces on a single statement if, strncpy over strscpy
• Add missing MODULE_PARM_DESC for test_mode
• Bump to 0.3.1

clang-format reported nothing, sources were already compliant.

Test plan

• Rebuild and load the module, confirm both cameras on a dual board stream. Verified on Orin NX, JetPack 6.2.2