Minor codebase improvements suggested by Sonarcloud

- src/modsecurity.cc
  - Replace the redundant type with "auto".
- src/transaction.cc
  - Avoid this unnecessary copy by using a "const" reference.
- test/common/custom_debug_log.cc
  - Use "=default" instead of the default implementation of this special
    member functions.
    - Removed the unnecessary destructor override instead.
  - Annotate this function with "override" or "final".
    - Removed the unnecessary destructor override instead.
  - Remove this "const" qualifier from the return type in all
    declarations.
- test/common/modsecurity_test_context.h
  - Replace the redundant type with "auto".
- test/regression/regression.cc
  - Use the "nullptr" literal.
  - Replace this declaration by a structured binding declaration.
  - Replace "reinterpret_cast" with a safer operation.

test/common/custom_debug_log.cc

@@ -23,8 +23,6 @@
 
 namespace modsecurity_test {
 
-    CustomDebugLog::~CustomDebugLog() {}
-
     void CustomDebugLog::write(int level, const std::string &message) {
         m_log << "[" << level << "] " << message << std::endl;
     }
@@ -36,13 +34,13 @@ namespace modsecurity_test {
         m_log << msgf << std::endl;
     }
 
-    bool const CustomDebugLog::contains(const std::string &pattern) const {
+    bool CustomDebugLog::contains(const std::string &pattern) const {
         modsecurity::Utils::Regex re(pattern);
         std::string s = m_log.str();
         return modsecurity::Utils::regex_search(s, re);
     }
 
-    std::string const CustomDebugLog::log_messages() const {
+    std::string CustomDebugLog::log_messages() const {
         return m_log.str();
     }
 

test/common/custom_debug_log.h

@@ -26,13 +26,12 @@ namespace modsecurity_test {
 class CustomDebugLog : public modsecurity::debug_log::DebugLog {
  public:
     CustomDebugLog *new_instance();
-    ~CustomDebugLog();
 
     void write(int level, const std::string& message) override;
     void write(int level, const std::string &id,
         const std::string &uri, const std::string &msg) override;
-    bool const contains(const std::string& pattern) const;
-    std::string const log_messages() const;
+    bool contains(const std::string& pattern) const;
+    std::string log_messages() const;
     std::string error_log_messages();
     int getDebugLogLevel() override;
 

test/common/modsecurity_test_context.h

@@ -31,8 +31,8 @@ namespace modsecurity_test {
 
     private:
         static void logCb(void *data, const void *msgv) {
-            const char *msg = reinterpret_cast<const char *>(msgv);
-            std::stringstream *ss = (std::stringstream *)data;
+            auto msg = reinterpret_cast<const char *>(msgv);
+            auto ss = reinterpret_cast<std::stringstream *>(data);
             *ss << msg << std::endl;
         }
     };