Investigate gas estimation inconsistancy for read_only executions

[Leo-Besancon]

In order to choose the best max_gas parameter for a given operation, the best way to estimate the gas consumtion is to simulate it with a read_only call / read_only execution.
The returned value of the read_only call contains the gas used.

It however seems that the gas estimation is too low, and need to be increased by ~20% in order for the "real" call to suceed without an OutOfGas error.

We should investigate why the estimated gas value is too low and fix it.