optimize default gas limit

When not using the estimated gas feature (globally and for functions where it is not manditory), we use a default gas limit of 4543760. This value is the same as that used by Arc automated tests and thus is assumed to work in the most anticipated cases.

This ticket is about trying to find the lowest number that till works, to potentially save users' money.

Start by locating where the default gas limit of 4543760 is defined and how the estimated-gas option is bypassed globally and for individual functions. Use the Arc automated tests and representative non-estimated calls to compare lower limits; done means identifying the lowest value that still works in the anticipated cases and updating the default accordingly.

Written by the indexing model from the issue text.