cargo: improve and unify function regexp

[masicn]

Far from complete but reasonable amount of function syntax added.
Partial(since matching still occurs twice) unification solves signature-name search discrepancies.

[psibi]

Thanks for adding tests! Is this ready to merge since you have mentioned in the PR description that it's "far from complete"? These days I use treesit-beginning-of-defun for a similar use case.

[masicn]

Thanks for adding tests! Is this ready to merge since you have mentioned in the PR description that it's "far from complete"? These days I use treesit-beginning-of-defun for a similar use case.

The commit is fully functional and safe enough.
Regexp is incomplete but it is an improvement to previous version.

Treesiter seems like proper solution though, thanks for pointing out, I have been using old customization without it.

[psibi]

Cool, thanks! Yeah, I have completely switched to treesitter now and I find it more reliable. Details here, if you want to switch: https://github.com/emacs-rustic/rustic?tab=readme-ov-file#tree-sitter

[masicn]

Cool, thanks! Yeah, I have completely switched to treesitter now and I find it more reliable. Details here, if you want to switch: https://github.com/emacs-rustic/rustic?tab=readme-ov-file#tree-sitter

Thank you for the merge and the instruction!