refactor(model): remove some indirection

For small fixed-size structures, it's better to use a slice of values, instead
of a slice of pointers to values: they're stored contiguously and thus can be
iterated on quickly by the CPU, and it does remove an indirection per object
every time the GC kicks in.

internal/model/user_session.go

@@ -30,7 +30,7 @@ func (u *UserSession) UseTimezone(tz string) {
 }
 
 // UserSessions represents a list of sessions.
-type UserSessions []*UserSession
+type UserSessions []UserSession
 
 // UseTimezone converts creation date of all sessions to the given timezone.
 func (u UserSessions) UseTimezone(tz string) {