A 28-year-old male from Delhi presents with a 3-month history of progressive cervical lymphadenopathy, fever, and night sweats. On examination, he has firm, non-tender, rubbery lymph nodes in the neck. A lymph node biopsy shows effacement of normal architecture with scattered large cells containing multiple nuclei and prominent nucleoli, surrounded by a rich inflammatory infiltrate of small lymphocytes, eosinophils, and histiocytes. Immunohistochemistry reveals CD30+ and CD15+ large cells that are CD45−, CD20−, and CD3−. What is the most likely diagnosis?