feat: some optimisations to circuits

[iAmMichaelConnor]

So far:

• Found a bug in array filtering, so increased the constraints to fix it (doh!)
• Shifted the key validation requests array, instead of filter it, to save 10k constraints. Relies on the assumption that key validation requests are processed in order, taking the first N requests from the left of the array each time. Is that a valid assumption?