Get a starting pitcher's first-inning (NRFI) splits for a season

MLB-only route. Returns the pitcher’s pitcher_f1 document from first_inning_stats — starts, inning-1 runs/earned runs allowed, F1 ERA (earned runs per 9 first innings), NRFI count and rate, and inning-1 K / H / BB. Run attribution follows responsible_pitcher_id, so a bequeathed runner who scores in the first breaks the starter’s NRFI. Players only — team-side first-inning splits surface through the NRFI card.