Fix: Update deprecated GitHub Actions and resolve subsequent build/test failures

- Updates `actions/checkout` and `actions/cache` to v4 in all workflows.
- Updates all build configurations in the CI to use modern, available versions of `gcc` (v11) and `clang` (v14), removing duplicate jobs.
- Removes the no-longer-available `valgrind-dbg` package from the build process.
- Fixes a `-Werror=overloaded-virtual` C++ compilation error by making the `operator()` in the test class virtual.
- Fixes a large number of `cpplint` errors across the codebase, primarily missing header includes.
- Implements a random port selection mechanism for the integration tests to prevent port conflicts, especially on macOS. This includes a new `test/test_utils.hpp` helper file.
- Adds a `perror` call to `webserver.cpp` to provide more detailed error information if the server daemon fails to start.
- Forces IPv4 on macOS to work around a suspected issue with `libmicrohttpd` and Unix domain sockets.

Author: google-labs-jules[bot]

src/webserver.cpp

@@ -293,6 +293,10 @@ bool webserver::start(bool blocking) {
         start_conf |= MHD_USE_IPv6;
     }
 
+#if defined(__APPLE__)
+    start_conf |= MHD_USE_IPv4;
+#endif
+
     if (use_dual_stack) {
         start_conf |= MHD_USE_DUAL_STACK;
     }

test/littletest.hpp

@@ -76,7 +76,7 @@
                 __lt_name__ = #__lt_test_name__; \
                 littletest::auto_test_vector.push_back(this); \
             } \
-            void operator()(littletest::test_runner* __lt_tr__) \
+            virtual void operator()(littletest::test_runner* __lt_tr__) \
             {
 
 #define LT_END_TEST(__lt_test_name__) \