fix: add missing manual_doc_id_mapping field in zstd test IndexSettings initializer

Struct literal was missing the new field introduced in the manual doc id
mapping refactor, causing a compile error under --all-features.

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

src/index/index_meta.rs

@@ -465,6 +465,7 @@ mod tests {
                     field: "text".to_string(),
                     order: Order::Asc,
                 }),
+                manual_doc_id_mapping: false,
                 docstore_compression: crate::store::Compressor::Zstd(ZstdCompressor {
                     compression_level: Some(4),
                 }),