fix: match jridgewell tie-break and preserve metadata in indexed maps

- Walk back/forward through duplicate-column segments so GLB returns
  earliest-equal and LUB returns latest-equal, matching
  @jridgewell/trace-mapping. Rust's binary_search_by_key returns an
  unspecified index among equal keys and previously broke drop-in
  parity when two segments shared a generated column.
- Indexed (sectioned) source maps now propagate debugId, x_* extensions,
  and sourceRoot from the outer map, and merge scopes from each section
  (offsetting generated ranges, remapping definition and source indices)
  instead of dropping them.

Author: BartWaardenburg