The Swift driver returns errors when users begin iterating a dead cursor:

for x in cursor {
    // no errors in here
}
print(cursor.next()) // LogicError("cannot iterate a dead cursor")

We should consider doing something similar in the Rust driver.

The rationale for doing so is that a user iterating a dead cursor is probably indicative of a programmer error:

• In the "eager" cursor, it could only happen if they're not using a while let loop or if they start iterating after their while let loop ended, both likely errors.
• In the "non-eager" case, it means they're not distinguishing between a cursor being exhausted and returning None, which is also usually an error since it can lead to infinite loops.