remove obsolete dead-code suppression from SGR loop

`_csiHandleSgr` carried a `// ignore: dead_code` directive with the
note "workaround for a bug in the analyzer". Re-running the
analyzer with the suppression removed produces no warning — Dart's
flow analysis has caught up since the comment was added.

Per the no-lint-suppression rule the suppression needed to be
either removed or given a more substantive justification; the
analyzer's silence makes the call easy.

Co-Authored-By: Claude <noreply@anthropic.com>

lib/src/terminal/src/core/escape/parser.dart

@@ -416,8 +416,6 @@ class EscapeParser {
       return handler.resetCursorStyle();
     }
 
-    // This is a workaround for a bug in the analyzer.
-    // ignore: dead_code
     for (var i = 0; i < _csi.params.length; i++) {
       final param = params[i];
       switch (param) {