feat(jet): add ExprPtrs for pointer slice expressions

ExprPtrs dereferences []*T values, skips nil entries, and maps survivors
through a converter.

Co-authored-by: Cursor <cursoragent@cursor.com>

doc.go

@@ -17,7 +17,7 @@
 //
 // Dialect-neutral type aliases ([Column], [ColumnList]) and helpers for column
 // lists ([NormalCols], [ContainsCol]) and expression building ([ExprValues],
-// [StringKSUIDExpr], [BinaryKSUIDExpr]).
+// [ExprPtrs], [StringKSUIDExpr], [BinaryKSUIDExpr]).
 // [QueryCount] and [BuildQueryCountFn] support pagination total counts.
 //
 // Partial-update helpers ([ApplyPtr], [ApplyVal]) track changed fields for