Show exec output on success with trimmed display (#4113)

- Refactor Exec Cell into its own module
- update exec command rendering to inline the first command line
- limit continuation lines
- always show trimmed output

codex-rs/tui/src/exec_cell/mod.rs

@@ -0,0 +1,12 @@
+mod model;
+mod render;
+
+pub(crate) use model::CommandOutput;
+#[cfg(test)]
+pub(crate) use model::ExecCall;
+pub(crate) use model::ExecCell;
+pub(crate) use render::OutputLinesParams;
+pub(crate) use render::TOOL_CALL_MAX_LINES;
+pub(crate) use render::new_active_exec_command;
+pub(crate) use render::output_lines;
+pub(crate) use render::spinner;