Set a limit on max recursions.

Applies to last remaining recursive calls in regex creation, and format string parsing.
Added tests, and updated CI.

test/bad_format_string.cpp

@@ -0,0 +1,32 @@
+/*
+ *
+ * Copyright (c) 2024
+ * John Maddock
+ *
+ * Use, modification and distribution are subject to 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)
+ *
+ */
+
+#include <iostream>
+#include <boost/regex.hpp>
+#include <boost/core/lightweight_test.hpp>
+
+int main()
+{
+   try{
+      std::string format_string("(((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((");
+      boost::regex e("foo");
+      std::string in("foobar");
+      std::string out;
+      boost::regex_replace(std::back_inserter(out), in.begin(), in.end(),
+         e, format_string, boost::match_default | boost::format_all);
+      BOOST_TEST(false);
+   }
+   catch (const std::runtime_error&)
+   {
+      std::cout << "OK" << std::endl;
+   }
+   return boost::report_errors();
+}