[v5.0] Replace cloop auto_ptr with unique_ptr

[dand-oss]

Use std::unique_ptr for cloop's local Generator owner. The pointer is only default-constructed, reset and dereferenced, so it does not require auto_ptr's transfer-on-copy behavior. unique_ptr also removes reliance on a facility removed from the C++ standard in C++17.

Master already uses unique_ptr after the cloop update in 30d835a; this small compatibility change targets v5.0-release and retains C++11 support.

Validation on Linux x86-64 with GCC 16.2:

• Built all six cloop source files before the change in C++11 mode.
• Built all six patched source files in C++11 and C++23 modes, with deprecated declarations treated as errors.
• The original and both patched binaries produce byte-for-byte identical test C headers, test C++ headers, and the Firebird IdlFbInterfaces.h header (675,564 bytes).
• git diff --check passes.

Windows validation and a complete Firebird 5 server build have not been run locally.