feat: a utility for creating "permutation views" (#2552)

I'm working on a lancedb version of pytorch data loading (and hopefully
addressing https://github.com/lancedb/lance/issues/3727).

However, rather than rely on pytorch for everything I'm moving some of
the things that pytorch does into rust. This gives us more control over
data loading (e.g. using shards or a hash-based split) and it allows
permutations to be persistent. In particular I hope to be able to:

* Create a persistent permutation
* This permutation can handle splits, filtering, shuffling, and sharding
* Create a rust data loader that can read a permutation (one or more
splits), or a subset of a permutation (for DDP)
* Create a python data loader that delegates to the rust data loader

Eventually create integrations for other data loading libraries,
including rust & node

python/src/table.rs

@@ -3,6 +3,7 @@
 use std::{collections::HashMap, sync::Arc};
 
 use crate::{
+    connection::Connection,
     error::PythonErrorExt,
     index::{extract_index_params, IndexConfig},
     query::{Query, TakeQuery},
@@ -249,7 +250,7 @@ impl Table {
 }
 
 impl Table {
-    fn inner_ref(&self) -> PyResult<&LanceDbTable> {
+    pub(crate) fn inner_ref(&self) -> PyResult<&LanceDbTable> {
         self.inner
             .as_ref()
             .ok_or_else(|| PyRuntimeError::new_err(format!("Table {} is closed", self.name)))
@@ -272,6 +273,13 @@ impl Table {
         self.inner.take();
     }
 
+    pub fn database(&self) -> PyResult<Connection> {
+        let inner = self.inner_ref()?.clone();
+        let inner_connection =
+            lancedb::Connection::new(inner.database().clone(), inner.embedding_registry().clone());
+        Ok(Connection::new(inner_connection))
+    }
+
     pub fn schema(self_: PyRef<'_, Self>) -> PyResult<Bound<'_, PyAny>> {
         let inner = self_.inner_ref()?.clone();
         future_into_py(self_.py(), async move {