chore: split decimal cast

[fansehep]

Which issue does this PR close?

Part of #5125

Rationale for this change

What changes are included in this PR?

Are there any user-facing changes?

[tustvold]

Could we instead put the decimal module underneath cast, as described in the ticket. i.e. create a directory called cast and place it under that?

[fansehep]

Could we instead put the decimal module underneath cast, as described in the ticket. i.e. create a directory called cast and place it under that?

I misunderstand the ticket. 😢

[tustvold]

Marking as draft to signify this is not waiting on review, feel free to unmark when you would like me to take another look