Checkpoint
One last thing before we move on. Same surface as a write step — but the lesson doesn't complete until this passes.
Checkpoint. Score a batch of leads with a weighted sum — the everyday
use of vectorization. Each row is a lead's features; weights has one
weight per feature. Write score_rows(rows, weights) returning a list
where each entry is sum(feature * weight) for that row.
Expected output:
[7.0, 8.0]