feat: adds isin support to the 'Expr' builder (#3523)

The `Expr` build already includes a lot of useful filtering options,
`eq, ne, gt/gte, lt/lte, and_, or_, contains, cast`, but is was missing
a membership like `isin`. This PR adds that support, as minimally as
possible, allowing easy filtering for membership in a list, without
needing to be a series of `where` expressions.

I didn't see anything in CONTRIBUTING.md about needing a feature request
or issue first, so I just made the change. My apologies if I missed that
somewhere.

Thanks for the vector store, we're using it now in paperless-ngx.

python/src/expr.rs

@@ -9,7 +9,9 @@
 
 use arrow::{datatypes::DataType, pyarrow::PyArrowType};
 use datafusion_common::ScalarValue;
-use lancedb::expr::{DfExpr, col as ldb_col, contains, expr_cast, lit as df_lit, lower, upper};
+use lancedb::expr::{
+    DfExpr, col as ldb_col, contains, expr_cast, is_in, lit as df_lit, lower, upper,
+};
 use pyo3::types::PyBytes;
 use pyo3::{Bound, PyAny, PyResult, exceptions::PyValueError, prelude::*, pyfunction};
 
@@ -105,6 +107,14 @@ impl PyExpr {
         Self(contains(self.0.clone(), substr.0.clone()))
     }
 
+    // ── membership ───────────────────────────────────────────────────────────
+
+    /// Return true where the value is one of the given expressions (SQL ``IN``).
+    fn isin(&self, list: Vec<Self>) -> Self {
+        let items: Vec<DfExpr> = list.into_iter().map(|e| e.0).collect();
+        Self(is_in(self.0.clone(), items))
+    }
+
     // ── type cast ────────────────────────────────────────────────────────────
 
     /// Cast the expression to `data_type`.