Fix rust releases

[felixhekhorn]

So we would need to release to actually see if it is working or not

Originally posted by @AkshatRai07 in #553 (comment)

• I made https://github.com/NNPDF/eko/releases/tag/v0.15.5 but some of the Mac workflows failed, can you please check? If it is just macos-aarch64 and that is tricky to solve, I'm happy do deactivate it for the moment and worry about whenever someone (@scarlehoff ) actually complains in real life because they need it
• The Linux C-API seems to have built fine https://github.com/NNPDF/eko/actions/runs/29902592251/job/88866562257 - but it is only at a random URL. Can we please change it such that if it is trigger on a (random) commit, it can be where ever - but if it is triggered on a tag, add it to the release page (as in PineAPPL https://github.com/NNPDF/pineappl/releases/tag/v1.4.2). (Side comment (mostly for myself): by the way this "forces" us to put always a GitHub Release and not just a tag. ) Also else how can we retrieve the file reliably?
• Linux workflow says "Uploaded bytes 6413953" ~ 6MB, is this true? PineAPPL is a factor of 10 lower ... yes we do contain more math, but that much?

[AkshatRai07]

Solution to 3 bugs:

• It was some network error and hence eko-rs did not got built for mac-aarch64. Now, I reran it and the release workflow is not working. Please change the permissions of PYPI_TOKEN to allow it to publish eko-rs, I think there's an option to allow token for certain/all projects.
• There is some MacOS linking issue, I will fix it.
• cargo-c was building the staticlib too, which is taking 22 MB of the 23 MB in the generated artifacts. We actually don't need that file, I'll do the necessary changes.