feat(cli): introduce flexible event row output formats and column selection

Replace fixed output modes with customizable table, CSV, TSV, and JSON Lines formats. This allows users to select specific data columns and control header visibility for better integration with scripts and monitoring tools.

crates/irtt-cli/tests/applet_dispatch.rs

@@ -51,7 +51,8 @@ fn canonical_client_subcommand_dispatches_to_client() {
 
     assert!(output.status.success(), "{text}");
     assert!(text.contains("Minimal IRTT-compatible stream client"));
-    assert!(text.contains("--output <OUTPUT>"));
+    assert!(text.contains("--format <FORMAT>"));
+    assert!(text.contains("--columns <COLUMNS>"));
 }
 
 #[cfg(unix)]
@@ -65,7 +66,8 @@ fn client_applet_name_dispatches_to_client() {
 
     assert!(output.status.success(), "{text}");
     assert!(text.contains("Minimal IRTT-compatible stream client"));
-    assert!(text.contains("--output <OUTPUT>"));
+    assert!(text.contains("--format <FORMAT>"));
+    assert!(text.contains("--columns <COLUMNS>"));
 }
 
 #[cfg(all(unix, feature = "tui"))]