Is your feature request related to a problem? Please describe.
This can be extremely useful.
A great feature
It isn't related to a problem,

Describe the solution you'd like
OptiFine version is like this,

"attachments": 
{ 

    "attachment_name": [tx, ty, tz]
  },

It can be like,

"attachments": 
  `{
    "attachment_name": [tx, ty, tz], 
    "attachment_name": [rx, ry, rz], 
    "attachment_name": [sx, sy, sz] 
  },` 

Does OptiFine do this
This feature is currently the latest feature from OptiFine. Thus it can change

Additional context
Items can be like

Just put the attachment inside an empty part, you can then rotate and scale that part normally and it will affect the attachment point inside it.

Adding attachment specific rotation and scales would just break optifine compat for no reason, when the above takes seconds to setup.

empty part?

I.e add a part/group inside left_arm that doesn't have any boxes and only an attachment point.

That part can then be rotated and scaled

just to be clear
like this?

or like

cant find the scale one for the one above

maybe i can do it with cem animations