It’s a turning point for 590 Madison Ave., the black granite tower at East 57th Street with a bamboo-filled atrium that attaches to Trump Tower. RXR and Elliott Investment Management purchased the 42-story, 1 million square-foot tower last year from longtime owner State Teachers Retirement System of Ohio for nearly $1.1 billion — the first Manhattan office property to break the billion-dollar sale threshold in three years. Scott Rechler-led RXR, the managing partner, set about preparing the