Add define BOOST_PARSER_DISABLE_TRACE to disable trace mode at compile time.

The trace feature doubles the compile time, even if never used.
This patch introduces the preprocessor define BOOST_PARSER_DISABLE_TRACE
to deactivate this feature at compile time.

test/disable_trace.cpp

@@ -0,0 +1,27 @@
+/**
+*   Copyright (C) 2025
+ *
+ *   Distributed under the Boost Software License, Version 1.0. (See
+ *   accompanying file LICENSE_1_0.txt or copy at
+ *   http://www.boost.org/LICENSE_1_0.txt)
+ */
+
+#define BOOST_PARSER_DISABLE_TRACE
+
+#include <boost/core/lightweight_test.hpp>
+#include <boost/parser/parser.hpp>
+
+int main()
+{
+    namespace bp = boost::parser;
+    {
+        auto const parser =
+            bp::string("FOO") >> -(bp::string("bar") | bp::string("foo"));
+
+        auto result = bp::parse("FOOfoo", parser);
+        BOOST_TEST(result);
+        BOOST_TEST(bp::get(*result, bp::llong<0>{}) == std::string("FOO"));
+        BOOST_TEST(bp::get(*result, bp::llong<1>{}) == std::string("foo"));
+    }
+    return boost::report_errors();
+}