fix all compiler warnings

src/main.rs

@@ -3,27 +3,20 @@
 #![feature(type_alias_impl_trait)]
 #![feature(impl_trait_in_assoc_type)]
 
-use ch32_hal::{embassy, pac::Interrupt::USB_LP_CAN1_RX0};
-use ch32_hal::usart;
 use embassy_executor::Spawner;
-use embassy_futures::join::join;
-use embassy_time::{Duration, Timer};
-use embassy_usb::UsbDevice;
-use embassy_usb::{Builder, Config, class::cdc_acm::{CdcAcmClass, State}};
-use hal::peripherals::USBD;
-use hal::gpio::{AnyPin, Level, Output, Pin};
-use hal::usart::UartTx;
-use hal::usbd::{Driver, Instance, InterruptHandler};
+use embassy_time::Timer;
 use hal::bind_interrupts;
+use hal::gpio::{Level, Output};
+use hal::peripherals::USBD;
+use hal::usbd::InterruptHandler;
 use {ch32_hal as hal, panic_halt as _};
 
 bind_interrupts!(struct Irqs {
    USB_LP_CAN1_RX0 => InterruptHandler<USBD>;
 });
 
-
 #[embassy_executor::main(entry = "qingke_rt::entry")]
-async fn main(spawner: Spawner) -> ! {
+async fn main(_spawner: Spawner) -> ! {
     let p = hal::init(Default::default());
 
     let mut led = Output::new(p.PB2, Level::Low, Default::default());