Refactor LPUART driver constructors (#51)

* Refactor LPUART driver constructors

- Add new_with_rtscts(), new_with_rts(), new_with_cts() methods
- Store RTS/CTS pins in TX/RX structs
- Remove enable_tx, enable_rx, enable_rx_rts, enable_tx_cts config fields
- Fix typo: msb_firs -> msb_first
- Fix write_byte() return type to Result<()>

* Update hello example for LPUART driver changes

* Refactor buffered LPUART initialization logic

- Split new_inner() into init_common() and separate helpers for full-duplex, TX-only, and RX-only
- Replace assert!() with proper Error::InvalidArgument returns for empty buffers
- Simplify constructor implementations by removing expect() calls

3 files changed, 8 insertions, 10 deletions

diff --git a/examples/src/bin/hello.rs b/examples/src/bin/hello.rs
index f426d1898..e371d9413 100644
--- a/examples/src/bin/hello.rs
+++ b/examples/src/bin/hello.rs
@@ -2,27 +2,29 @@
 #![no_main]
 
 use embassy_executor::Spawner;
+use embassy_mcxa::clocks::config::Div8;
 use hal::lpuart::{Blocking, Config, Lpuart};
 use {defmt_rtt as _, embassy_mcxa as hal, panic_probe as _};
 
 /// Simple helper to write a byte as hex to UART
 fn write_hex_byte(uart: &mut Lpuart<'_, Blocking>, byte: u8) {
     const HEX_DIGITS: &[u8] = b"0123456789ABCDEF";
-    uart.write_byte(HEX_DIGITS[(byte >> 4) as usize]);
-    uart.write_byte(HEX_DIGITS[(byte & 0xF) as usize]);
+    let _ = uart.write_byte(HEX_DIGITS[(byte >> 4) as usize]);
+    let _ = uart.write_byte(HEX_DIGITS[(byte & 0xF) as usize]);
 }
 
 #[embassy_executor::main]
 async fn main(_spawner: Spawner) {
-    let p = hal::init(hal::config::Config::default());
+    let mut cfg = hal::config::Config::default();
+    cfg.clock_cfg.sirc.fro_12m_enabled = true;
+    cfg.clock_cfg.sirc.fro_lf_div = Some(Div8::no_div());
+    let p = hal::init(cfg);
 
     defmt::info!("boot");
 
     // Create UART configuration
     let config = Config {
         baudrate_bps: 115_200,
-        enable_tx: true,
-        enable_rx: true,
         ..Default::default()
     };
 
@@ -97,7 +99,7 @@ async fn main(_spawner: Spawner) {
             // Regular character
             buffer[buf_idx] = byte;
             buf_idx += 1;
-            uart.write_byte(byte);
+            let _ = uart.write_byte(byte);
         }
     }
 }
diff --git a/examples/src/bin/lpuart_buffered.rs b/examples/src/bin/lpuart_buffered.rs
index 7f77d557d..420589d00 100644
--- a/examples/src/bin/lpuart_buffered.rs
+++ b/examples/src/bin/lpuart_buffered.rs
@@ -27,8 +27,6 @@ async fn main(_spawner: Spawner) {
     // UART configuration (enable both TX and RX)
     let config = Config {
         baudrate_bps: 115_200,
-        enable_tx: true,
-        enable_rx: true,
         rx_fifo_watermark: 0,
         tx_fifo_watermark: 0,
         ..Default::default()
diff --git a/examples/src/bin/lpuart_polling.rs b/examples/src/bin/lpuart_polling.rs
index 9cea418cc..b80668834 100644
--- a/examples/src/bin/lpuart_polling.rs
+++ b/examples/src/bin/lpuart_polling.rs
@@ -19,8 +19,6 @@ async fn main(_spawner: Spawner) {
     // Create UART configuration
     let config = Config {
         baudrate_bps: 115_200,
-        enable_tx: true,
-        enable_rx: true,
         ..Default::default()
     };