Changed default wrap algorithm from OptimalFit to FirstFit (#7960)

Codex identified this as the cause of a reported hang:
https://github.com/openai/codex/issues/7822. Apparently, the wrapping
algorithm we're using has known issues and bad worst-case behaviors when
OptimalFit is used on certain strings. It recommended switching to
FirstFit instead.

codex-rs/tui2/src/markdown_render.rs

@@ -595,8 +595,8 @@ mod tests {
             lines,
             vec![
                 "- outer item with".to_string(),
-                "  several words".to_string(),
-                "  to wrap".to_string(),
+                "  several words to".to_string(),
+                "  wrap".to_string(),
                 "    - inner item".to_string(),
                 "      that also".to_string(),
                 "      needs wrapping".to_string(),