libcamera: request: Add a toString()

Provide a toString helper to assist in printing Request state
for debug and logging contexts.

Reviewed-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Signed-off-by: Kieran Bingham <kieran.bingham@ideasonboard.com>

include/libcamera/request.h

@@ -10,6 +10,7 @@
 #include <map>
 #include <memory>
 #include <stdint.h>
+#include <string>
 #include <unordered_set>
 
 #include <libcamera/class.h>
@@ -56,6 +57,8 @@ public:
 
 	bool hasPendingBuffers() const { return !pending_.empty(); }
 
+	std::string toString() const;
+
 private:
 	LIBCAMERA_DISABLE_COPY(Request)