feat: New Instruction addi "Add-Immediate"

[aszepieniec]

This PR adds an instruction addi which takes an immediate argument and adds it to the top of the stack. This addresses a pattern identified by @aszepieniec but with a different solution. The main motivation is to anticipate computing the AIR circuits on an out-of-domain row located at a dynamically known address. The merits of this PR should be considered in combination of future PRs that accomplish that feat.

The word dynamic is key, because the current auto-generated tasm code hardcodes the location of the out-of-domain row to a statically known address. While that solution is more efficient in terms of tasm instruction count, it is also less versatile. In particular, it requires static memory layouts for all proofs to be verified by a program. This requirement makes certain patterns impossible, such as verifying proofs in a dynamic loop.

This instruction reduces the cost of switching to dynamic out-of-domain row locations.

In order to get the right address on top of the stack:

• with static addresses: push [static_address]
• with dynamic addresses, before this PR: dup x push [static_offset] add
• with dynamic addresses, after this PR: dup x addi [static_offset]