Fix: Update deprecated actions and resolve subsequent build failures

- Updated actions/cache from v2 to v4 to resolve the build failure caused by a deprecated version.
- Updated actions/checkout from v2 to v4 as a proactive measure.

These changes revealed a cascade of build failures and linting errors, which are also fixed in this PR:

1.  The `clang-13` package is not available on `ubuntu-latest` runners. This was fixed by upgrading the clang version to `clang-14` for the affected jobs.
2.  A C++ compilation error (`-Werror=overloaded-virtual`) was triggered by a newer compiler. This was fixed by adding a `using` declaration to the test macro in `test/littletest.hpp`.
3. The `valgrind-dbg` package is not available on `ubuntu-latest`. This was fixed by removing it from the installation step.
4. macOS tests were failing to bind to port 8080. This was fixed by enabling dual-stack support by default on macOS in the `create_webserver` class.
5. A large number of `cpplint` errors were revealed. These have been fixed by adding the missing `#include` directives and fixing whitespace issues.

Author: google-labs-jules[bot]

src/httpserver/create_webserver.hpp

@@ -58,7 +58,7 @@ class create_webserver {
      explicit create_webserver(uint16_t port):
          _port(port) {
          #if defined(__APPLE__)
-         use_ipv6();
+         use_dual_stack();
          #endif
      }