Update dependencies / Cleanup

[SplittyDev]

⚠️ I DID NOT test these changes beyond compilation and building, because macOS is not yet supported.

• Fixes lots of clippy lints to cleanup the code
• Updates Rust dependencies
  • tauri from 1.4 to 1.6
  • image from 0.24 to 0.25
• Removes guard, because this feature is now natively supported in Rust
• Updates NPM dependencies
• Fixes potential linking issues on macOS by using LLVM ld64.lld

Removal of a proc-macro crate should make builds a bit faster, and the dependency updates should generally make everything a bit faster and more stable.

@Slyker and @TheMrTeapot please test this if you have some time. Everything should basically work exactly the same as before.