parser: implement for loops, port for/while loop test

Implement in parser.c:
- forPrefix: parse for input expressions and capture variables
- parseForExpr: for_simple and for AST nodes with optional else
- Handle for and while in parsePrimaryTypeExpr for top-level usage

Remove stale cppcheck knownConditionTrueFalse suppression.

Port test "top-level for/while loop".

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

parser_test.zig

@@ -624,6 +624,17 @@ test "zig fmt: respect line breaks before functions" {
     );
 }
 
+test "zig fmt: top-level for/while loop" {
+    try testCanonical(
+        \\for (foo) |_| foo
+        \\
+    );
+    try testCanonical(
+        \\while (foo) |_| foo
+        \\
+    );
+}
+
 test "zig fmt: simple top level comptime block" {
     try testCanonical(
         \\// line comment