Update scaling to ensure parity with dotnet output

[donaldgray]

In production use, noticed that there are differences between the sizes calculated by the iiif-net dotnet library used by Protagonist and the sizes calculated by Appetiser.

Altered the scaled_dimensions_to_fit() function to use method from "old" Appetiser equivalent function https://github.com/dlcs/appetiser/blob/1.5.0/app/jp2/image.py#L218-L241 and used similar handling to dotnet code for w, and ,h.

For reference the dotnet lib functions are:

• https://github.com/digirati-co-uk/iiif-net/blob/main/src/IIIF/IIIF/Size.cs#L126-L139 (in this case these are for for w, and ,h)
• https://github.com/digirati-co-uk/iiif-net/blob/main/src/IIIF/IIIF/Size.cs#L111-L120 (for !w,h).

Note

How can we extend the test suite to allow us to test this function to ensure any future changes don't break anything (e.g. if we allow mutating size-parameters?

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@tomcrane conducted some tests: https://github.com/tomcrane/appetiserscale/blob/main/8-b-numbers.txt to check fix, based on https://github.com/tomcrane/appetiserscale/blob/main/test.py#L80