Fixed compilation errors in Span constructors by adding missing `column: None` field.
Verified that the existing multi-output CLI parsing implementation meets all
acceptance criteria for bead pdftract-37qim.
Changes:
- crates/pdftract-core/src/span/mod.rs: Add column field to new() and empty() constructors
Verification:
- All 23 output::tests pass
- CLI parsing validated for duplicate format detection, ndjson exclusivity, stdout uniqueness
- Format auto-naming (--format with -o) works correctly
- Default behavior (no flags -> JSON to stdout) confirmed
See notes/pdftract-37qim.md for detailed verification results.
Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>