SPK/PCK singleton structure now raising errors during compilation

[dahlend]

Rust intrinsically does not like the singletons kete uses.

In a recent update, they have officially started raising warnings when things are built the way that they are built here.
Due to a setting in kete, warnings of this type are automatically converted to errors, breaking compilation.

Realistically rust is 100% correct here, and kete is doing some funny business with memory, however the way it is currently built this is essentially impossible to cause issues unless someone does something with multi-threading and loading files simultaneously. Even then I am not convinced this will lead to issues.

Solutions

• Add an #[allow] at the correct spot to suppress the warning (probably ok?).
• Consider restructuring the singletons to make it more memory safe (definitely ok).

[dahlend]

This is temporarily fixed by #161 by adding #[allow], but at some point it would be good to look at this in more depth.