fix: Add timeout to write_serial to prevent hang on hardware without COM1

The while loop waiting for TX buffer ready would hang forever if COM1
doesn't exist. Added 10000 iteration timeout - silently skips if reached.

Author: J-x-Z

esp/EFI/BOOT/BOOTX64.EFI

@@ -61,12 +61,20 @@ pub fn is_data_ready() -> bool {
 }
 
 /// Write a byte to serial port (for stdout output)
+/// Has timeout to prevent hanging on hardware without COM1
 pub fn write_serial(byte: u8) {
     unsafe {
         let mut port_lsr = Port::<u8>::new(COM1 + 5);
-        // Wait for transmit buffer to be empty
-        while port_lsr.read() & 0x20 == 0 {}
-        let mut port_data = Port::<u8>::new(COM1);
-        port_data.write(byte);
+        // Wait for transmit buffer to be empty (with timeout)
+        let mut timeout = 10000u32;
+        while port_lsr.read() & 0x20 == 0 && timeout > 0 {
+            timeout -= 1;
+        }
+        if timeout > 0 {
+            let mut port_data = Port::<u8>::new(COM1);
+            port_data.write(byte);
+        }
+        // If timeout reached, silently skip (no COM1 available)
     }
 }
+