Deletion-vector writer + RowDelta action

### Is your feature request related to a problem or challenge?

iceberg-rust cannot produce v3 deletes today; only FastAppend exists.

### Describe the solution you'd like

_No response_

### Willingness to contribute

Yes

Start by tracing the existing FastAppend implementation in iceberg-rust and identify how write actions are represented. The work is complete when the writer can produce v3 deletes using deletion vectors and emits the RowDelta action.

Written by the indexing model from the issue text.