chore: clean Rust warnings and remove unused deps

- Remove serde_yaml and tokio from Cargo.toml (unused)
- Add #[allow(dead_code)] to utility code kept for future use
  (CUT_FULL, ALIGN_RIGHT, line(), PrinterError, SupabaseError,
   atualizar_sync, remover, Lock variant)
- Zero compiler warnings on release build

src-tauri/src/plugins/printer.rs

@@ -5,6 +5,7 @@ use std::sync::Mutex;
 use thiserror::Error;
 
 #[derive(Error, Debug)]
+#[allow(dead_code)]
 pub enum PrinterError {
     #[error("Impressora não encontrada. Verifique se está conectada via USB e ligada.")]
     NotFound,