currently, only SQL string predicate is supported:
https://github.com/lance-format/lance/blob/main/rust/lance/src/dataset/write/delete.rs#L82
the scanner creates a SQL expression filter:
https://github.com/lance-format/lance/blob/main/rust/lance/src/dataset/scanner.rs#L1162
which calls into parse_filer() and convert the SQL to datafusion expression:
https://github.com/lance-format/lance/blob/main/rust/lance-datafusion/src/planner.rs#L845

instead, i would suggest passing a datafusion expression directly into the table deletion API, so no conversion is needed (similarly, to how the query filter work, where they support both SQL and Expr)