Switch to indexed serialization

Switch column from sequence to indexed serialization. The difference is
that sequence stores data as a sequence of (length, data) and indexed puts
all lengths first, followed by all data. We expect this to be more
efficient if we do not read all data, or repeatedly borrow its serialized
representation.

For details, see frankmcsherry/columnar#30

Signed-off-by: Moritz Hoffmann <mh@materialize.com>

Author: antiguru

src/timely-util/src/containers.rs

@@ -547,6 +547,16 @@ mod tests {
 
     #[mz_ore::test]
     fn test_column_from_bytes() {
+        {
+            let mut column: Column<i32> = Default::default();
+            column.push_into(1);
+            column.push_into(2);
+            column.push_into(3);
+            let mut data = Vec::new();
+            column.into_bytes(&mut std::io::Cursor::new(&mut data));
+            println!("data: {:?}", data);
+        }
+
         let raw = raw_columnar_bytes();
 
         let buf = vec![0; raw.len() + 8];