fix(components/execd): support CR-delimited output and add tests

[Pangjiping]

Summary

• Add a custom Scanner.Split that treats both \n and \r as delimiters (handling \r\n as one) to capture progress outputs, and raise the max token size to 5MB to avoid truncating long lines.
• Add unit tests covering CR/LF splitting, incremental reads, and long-line handling.

Testing

• Not run (explain why)
• Unit tests
• Integration tests
• e2e / manual verification

Breaking Changes

• None
• Yes (describe impact and migration path)

Checklist

• Linked Issue or clearly described motivation
• Added/updated docs (if needed)
• Added/updated tests (if needed)
• Security impact considered
• Backward compatibility considered

[hittyt]

LGTM