Fix the remote player interpolation in a co-op game

In your co-op game, remote players snapped to each new server position as it arrived, about 15 times a second, so they rubber-banded at 60 frames a second. The fix keeps a buffer of timestamped snapshots, draws remote players slightly in the past, and blends between the two snapshots around that time.

An assistant wrote interpolate_remote_position(snapshot_times, snapshot_xs, now, interp_delay). It is in the editor. It has a bug. Find it and fix it.

Input and output:

• snapshot_times, snapshot_xs: the buffered snapshots, read in pairs: snapshot i says the player was at snapshot_xs[i] at time snapshot_times[i]. Times are in ascending order.
• now: the current time. interp_delay: how far in the past to draw.
• Return the position to draw.

Rules the tests check:

• If the two lists differ in length, use only as many snapshots as the shorter one has. With no snapshots, return 0.
• The render time is now - interp_delay.
• At or before the first snapshot's time, return the first position.
• At or after the last snapshot's time, return the last position. Never guess beyond the newest snapshot.
• Otherwise find the first snapshot i + 1 whose time is at or after the render time, and blend linearly between snapshots i and i + 1. If those two have the same time, return the position of i + 1.
• Answers within 0.000001 of the expected value pass.