fix(ci): remove redundant std::move in StreamingSink::create return

GCC -Wredundant-move with -Werror fails CI on Ubuntu 24.04.
NRVO handles the move automatically; explicit std::move is unnecessary.

Author: Johnson-Ogundeji

include/signet/ai/streaming_sink.hpp

@@ -474,7 +474,7 @@ class StreamingSink {
         const bool auto_start = impl->opts_.auto_start;
         StreamingSink sink(std::move(impl));
         if (auto_start) sink.impl_->start();
-        return std::move(sink);  // StreamingSink is movable (unique_ptr<Impl>)
+        return sink;  // NRVO — std::move is redundant here (GCC -Wredundant-move)
     }
 
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