Scale array MUST have the same dtype

[constantinpape]

The current v0.4 spec does not explicitly require that the scale arrays of one image to have the same dtype.
I think this should be fixed ASAP, since having different datatypes will make the data invalid for many tools. (In particular we know that this is the case for MoBIE, and I assume it's the case for most tools written in a strongly typed language).

We have discussed this before, and we're running into this issue with real data now. I am happy to propose the changes for this, but I didn't have time to keep up with all the latest spec developments; should the PR go to latest or is there something to take care of w.r.t. other current PRs?

[will-moore]

I think this is a duplicate of #2?
This is a small change and doesn't affect or conflict with other changes so I think it can be included in the v0.5 spec.

Although this isn't something we can validate with a JSON schema, I should be able to get ome-ngff-validator to check this and warn as Invalid for v0.5 spec. Noted at ome/ome-ngff-validator#6

[constantinpape]

Closed in favor of #2. (And PR is open #154)