Comprehensive analysis of four diagnostic file formats:
1. Compiler/Build Output Format (plain text with structured warnings)
2. Cargo Build Stderr Format (key-value pairs with cargo:warning= prefix)
3. JSON Debug Output Format (schema-versioned structured data)
4. Expected Diagnostics Format (test fixture expectations)
All formats use ASCII/UTF-8 encoding with Unix line endings (\n).
Verified encoding via hexdump analysis of multiple file types.
