Javadoc
For all these getters, returns the value at 'colIdx' and advances to the next
value. This must be called in lock-step with Records.next(). This is optimized
for the common case where the caller will read every value of every record.
It is invalid to call next*() for a subset of the records.
The type of the column must match. Undefined behavior if it does not match
or if called on a value that is NULL. (We don't want to verify because this
is the hot path.)
TODO: add a DEBUG mode which verifies the API is being used correctly.