Fix sorting citation by citation number

[lluchs]

Citations with citation numbers currently aren't sorted properly, for example output from the test in the second commit:

Expected:
[1]–[4]
[1]–[4]

Got:
[1]–[4]
[2], [1], [4], [3]

This PR defers sorting the citations until finish is called and the citation numbers are determined.

[AnsgarLichter]

I just wondered why my citations are not sorted properly and I have these weird combinations sometimes. Thanks for your PR, now I know that I should have configured my CSL in the right way. Hope this gets merged soon 👍

[Enivex]

I believe this would close https://github.com/typst/hayagriva/issues/115

[PgBiel]

Thank you! :blue_heart: