Allow the use of CSL's number-of-pages number variable

[Andrew15-5]

In BibTeX it looks like there is only the pages field and in CSL there are page and number-of-pages.

When I was testing Hayagriva is Typst with a custom CSL style I noticed that apparently Hayagriva's page-total is mapped to CSL's number-of-pages, but number-of-pages directly in the YAML file is not accessible. I don't see a reason to create a 3rd name for the same thing just to confuse CSL style developers. Why page-total is not named number-of-pages? I used volume until this moment, because I thought that number-of-pages just isn't supported yet. But it is, you just have to use non-CSL-standard page-total.

I want to either be allowed to use both fields (one is described here, and the other is inherited implicitly from CSL standard) that will map to the same CSL field/variable (i.e., aliases), or rename page-total to number-of-pages.