Trent Williams and the 49ers are at an impasse.  ESPN’s Adam Schefter reported Tuesday that the two sides are currently “struggling to find a contractual solution” with the star offensive lineman set to carry a $39 million cap hit next season.  “If the two sides can’t bridge their differences in their standoff, Williams would be expected to join this year’s free-agent class, making him one of the premier players available,” Schefter added.  The loss of Williams, who, even at 37 years old,