Removed unsafe from uarte

The constructors themselves are not strictly unsafe. Interactions with DMA can be generally unsafe if a future is dropped, but that's a separate issue. It is important that we use the `unsafe` keyword diligently as it can lead to confusion otherwise.

examples/nrf/src/bin/buffered_uart.rs

@@ -24,23 +24,21 @@ async fn main(_spawner: Spawner, p: Peripherals) {
 
     let irq = interrupt::take!(UARTE0_UART0);
     let mut state = State::new();
-    let u = unsafe {
-        BufferedUarte::new(
-            &mut state,
-            p.UARTE0,
-            p.TIMER0,
-            p.PPI_CH0,
-            p.PPI_CH1,
-            irq,
-            p.P0_08,
-            p.P0_06,
-            NoPin,
-            NoPin,
-            config,
-            &mut rx_buffer,
-            &mut tx_buffer,
-        )
-    };
+    let u = BufferedUarte::new(
+        &mut state,
+        p.UARTE0,
+        p.TIMER0,
+        p.PPI_CH0,
+        p.PPI_CH1,
+        irq,
+        p.P0_08,
+        p.P0_06,
+        NoPin,
+        NoPin,
+        config,
+        &mut rx_buffer,
+        &mut tx_buffer,
+    );
     pin_mut!(u);
 
     info!("uarte initialized!");