Ignore malformed ffprobe stream lines

[Mirochill]

Summary

• Ignore ffprobe stream output lines that are not key=value pairs so multi-line side data does not crash FFStream parsing.
• Preserve values after the first = and add a regression for side-data-style lines.

Fixes #19

Validation

• git diff --check
• git diff --cached --check
• git show --check --oneline HEAD
• Not run locally beyond the static Git checks above.