Mario Ferraro will spend his mid-20s in San Jose after the Sharks announced Thursday that they’ve signed the restricted free agent defenseman to a four-year contract. The 23-year-old Ferraro, who became an alternate captain for the Sharks last season, has grown into one of San Jose’s most reliable players on the blue line since debuting for the team in 2019-20. He stands to take on a more important role after the Sharks traded Brent Burns to Carolina last month, likely on the Sharks’ top defensive pairing. “Mario has shown that he is a dynamic and reliable defenseman for our club, skating top-…