API improvement: batches_to_flight_data forces clone

[amunra]

The API is pretty inconsistent, sometimes requiring a Schema and sometimes a SchemaRef.

For example I hold a SchemaRef, but batches_to_flight_data requires a Schema, forcing me to create a clone of the ref counted object.

Instead, the function should just take a &Schema.

pub fn batches_to_flight_data(
    schema: Schema,
    batches: Vec<RecordBatch>,
) -> Result<Vec<FlightData>, ArrowError> {
    let options = IpcWriteOptions::default();
    let schema_flight_data: FlightData = SchemaAsIpc::new(&schema, &options).into();
                                                          ^___ it's borrowed later anyways!

[jackwener]

Make sense to me