[feat] ivec struct api operations

[duarm]

Problem

there are no functions for ivec struct api (ivec2, ivec3, ivec4), like _add and _sub

Solution

Bring everything it makes sense from the ivec array api to the ivec struct api

Notes

• Lots of function across ivec2, ivec3, ivec4, might be better to split each type on a different PR

[recp]

Hi @duarm

It would be great to have the work! 😊

Thanks