feat: make find_files public (#1560)

# Description
Make the find_files API public, same as public API for connectors'
[`markFilesAsRead`](https://delta-io.github.io/connectors/latest/delta-standalone/api/java/io/delta/standalone/OptimisticTransaction.html#markFilesAsRead-io.delta.standalone.expressions.Expression-):


# Related Issue(s)
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closes #1559

# Documentation

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Co-authored-by: Will Jones <[email protected]>

rust/src/delta_datafusion.rs

@@ -1085,7 +1085,9 @@ impl TreeNodeVisitor for FindFilesExprProperties {
     }
 }
 
-pub(crate) struct FindFiles {
+/// Representing the result of the [find_files] function.
+pub struct FindFiles {
+    /// A list of `Add` objects that match the given predicate
     pub candidates: Vec<Add>,
     /// Was a physical read to the datastore required to determine the candidates
     pub partition_scan: bool,
@@ -1289,7 +1291,8 @@ pub(crate) async fn scan_memory_table(
     join_batches_with_add_actions(batches, map)
 }
 
-pub(crate) async fn find_files<'a>(
+/// Finds files in a snapshot that match the provided predicate.
+pub async fn find_files<'a>(
     snapshot: &DeltaTableState,
     object_store: ObjectStoreRef,
     schema: Arc<ArrowSchema>,