Replace manual snapshot tests with insta

[XAMPPRocky]

While looking into some of the generated code, and seeing if lazy_static could be replaced with std::sync::LazyLock (it can't currently), I noticed the setup in rasn-compiler-tests. Currently if you make a change to the generated code, every single instance of the tests needs to be manually updated. I think it would be better if these tests were moved to using insta, because that would allow for updating generated tests automatically in a single command and provide better error messages.

https://docs.rs/insta/latest/insta/

[6d7a]

Thank you for your idea. insta would indeed be a substantial improvement for the testing setup in rasn-compiler-tests. I'll put it on my list. PRs will be much appreciated.