As Sirens officials review this past PWHL season, they see a lot of progress. The Sirens averaged 4,019 fans in their 12 games at Prudential Center, a 45 percent increase from the previous season. They also set a U.S. professional women’s hockey record last month when they drew a sellout crowd of 18,006 fans at Madison Square Garden. Sirens head coach Greg Fargo (center) looks up a the scoreboard during a game this past season. Bill Kostroun for New York Post The team has an exciting, young core of back-to-back No. 1 overall picks in Sarah Fillier and Kristýna Kaltounková, as well as 2025-26 Rookie of the Year candidate Casey O’Brien. All that sounds good, but there’s a palpable sense of frustration with the Sirens, who failed to reach the postseason for the third consecutive year. The Sirens were finishing up exit interviews last week and preparing for yet another offseason of uncertainty as the Walter Cup playoffs started.…