Script Generator: Estimate time based on other rows in the script generator

As a script definition writer, I would like to be able to access all of the rows in some way in the time estimation function, so that scientists can make the estimated time-dependent on previous rows (this is important where ramps of temperature/field etc can take a long time).

## Acceptance Criteria

- [ ] I can use values from other rows in the script generator in my time estimation function

## Notes

- If it is easy to make this generalisable for other methods such as validation then that would also be great