deploy.json already has "init" for systems.
But systems are contracts. Scripts are best run through libraries.

Example:
An expensive addItem function, which adds a game item prototype with all its properties. Say it costs 1mil gas per item. I have an initializer which adds 100 of those. 100mil gas exceeds the limit.

• If the 100 adds are in a system contract, it will revert. And making a bunch of wrapper init systems is a really bad idea.
• If the 100 adds are in a library, forge script can at least split it into several transactions. But also the real contract calls (component sets) use only a small portion of all that gas.

(this is a simplified edge case, my real use case is unfinished and more convoluted, but similar enough, e.g. InitEquipmentAffixSystem uses way more than the transaction gas limit)

I tested that it minimally works via a slightly modified emojimon, if you wanna just clone it.

Some concerns:

• libs may not be the best name, open to suggestions
• The whole idea of modifying LibDeploy may be a bit too hardcodey. Maybe having a user-controllable Deploy.sol would be best. But that's way beyond the scope of this simple PR. (feat(cli): allow arbitrary project structure for LibDeploy and system types #309 kinda goes in that direction a bit, making scripts more local)