With Bill & Ted's Excellent Adventure turning 30 years old this month—older than both Keanu Reeves and Alex Winter were when they starred in the title roles—I recently fired up that most righteous time-travel comedy to see how well it holds up. While it does remain a perfectly charming, surprisingly funny little 90-minute movie, I was mainly surprised at the ways it's absolutely fascinating as just, like, a pop culture artifact that exists in this world. The first Bill & Ted is a perfect snapshot of a very specific moment in time, for better …