feat: hook up new writer for insert (#3029)

This hooks up a new writer implementation for the `add()` method. The
main immediate benefit is it allows streaming requests to remote tables,
and at the same time allowing retries for most inputs.

In NodeJS, we always convert the data to `Vec<RecordBatch>`, so it's
always retry-able.

For Python, all are retry-able, except `Iterator` and
`pa.RecordBatchReader`, which can only be consumed once. Some, like
`pa.datasets.Dataset` are retry-able *and* streaming.

A lot of the changes here are to make the new DataFusion write pipeline
maintain the same behavior as the existing Python-based preprocessing,
such as:

* casting input data to target schema
* rejecting NaN values if `on_bad_vectors="error"`
* applying embedding functions.

In future PRs, we'll enhance these by moving the embedding calls into
DataFusion and making sure we parallelize them. See:
https://github.com/lancedb/lancedb/issues/3048

---------

Co-authored-by: Claude Opus 4.6 <noreply@anthropic.com>

python/src/table.rs

@@ -7,6 +7,7 @@ use crate::{
     error::PythonErrorExt,
     index::{extract_index_params, IndexConfig},
     query::{Query, TakeQuery},
+    table::scannable::PyScannable,
 };
 use arrow::{
     datatypes::{DataType, Schema},
@@ -25,6 +26,8 @@ use pyo3::{
 };
 use pyo3_async_runtimes::tokio::future_into_py;
 
+mod scannable;
+
 /// Statistics about a compaction operation.
 #[pyclass(get_all)]
 #[derive(Clone, Debug)]
@@ -293,12 +296,10 @@ impl Table {
 
     pub fn add<'a>(
         self_: PyRef<'a, Self>,
-        data: Bound<'_, PyAny>,
+        data: PyScannable,
         mode: String,
     ) -> PyResult<Bound<'a, PyAny>> {
-        let batches: Box<dyn arrow::array::RecordBatchReader + Send> =
-            Box::new(ArrowArrayStreamReader::from_pyarrow_bound(&data)?);
-        let mut op = self_.inner_ref()?.add(batches);
+        let mut op = self_.inner_ref()?.add(data);
         if mode == "append" {
             op = op.mode(AddDataMode::Append);
         } else if mode == "overwrite" {