Use the merged base edition API in the layout benchmark writer

CI run 38936290519 failed before timing: rewrite_list_layout still called
WriteStrategyBuilder::with_list_layout(), removed by upstream #10563 and
inherited through the merged #10540 base. Keep the base's edition-driven
writer policy and adapt the benchmark helper instead of restoring the API.

Enable the experimental list edition only for list/list-elements modes.
Flat mode leaves it disabled, preserving the flat control. Drop the obsolete
environment guard and explicit writer toggle. Scanner runtime is unchanged,
so the completed local 48-case merged-comparison remains applicable.

Validation: built both release_debug examples with --locked; rewrote all
1,000,000 rows in flat, list, list-elements/1 MiB and list-elements/64 KiB
modes; all four full Arrow equality and layout-kind checks passed, as did
four V2 selection comparisons against full V1 scans followed by take.
Pinned formatting and diff whitespace checks passed. No new Rust-library
checks were needed for this example-only API adaptation.

Signed-off-by: Joe Isaacs <joe.isaacs@live.co.uk>

Author: joseph-isaacs

vortex/examples/rewrite_list_layout.rs

@@ -72,23 +72,18 @@ async fn main() -> Result<()> {
         matches!(args[2].as_str(), "flat" | "list" | "list-elements"),
         "Unknown layout"
     );
-    ensure!(
-        std::env::var("VORTEX_EXPERIMENTAL_LIST_LAYOUT").as_deref() != Ok("1"),
-        "Unset VORTEX_EXPERIMENTAL_LIST_LAYOUT so the flat control stays flat"
-    );
     let target_bytes = args.get(3).map(|value| value.parse::<u64>()).transpose()?;
     ensure!(target_bytes != Some(0), "TARGET_BYTES must be positive");
     let session = VortexSession::default().with_tokio();
     session.register_edition(&EXPERIMENT_EDITION)?;
-    session.enable_edition(EXPERIMENT_EDITION.edition.id)?;
+    if args[2] != "flat" {
+        session.enable_edition(EXPERIMENT_EDITION.edition.id)?;
+    }
     let input = session
         .open_options()
         .open_path(Path::new(&args[0]))
         .await?;
     let mut strategy = WriteStrategyBuilder::from_session(&session);
-    if args[2] == "list" {
-        strategy = strategy.with_list_layout();
-    }
     if let Some(target_bytes) = target_bytes {
         strategy = strategy.with_data_block_target_bytes(Some(target_bytes));
     }