fix(boards): BUSY pin pull-down → none on nRF SX1262 boards

SX1262's BUSY pin has an internal 20 kΩ pull-up (datasheet page 53).
Our Input::new(..., Pull::Down) on BUSY creates contention with that
internal pull-up, leaving BUSY at an indeterminate voltage. This can
cause wait_on_busy to mis-read the chip's ready state — sometimes
commands land while the chip is still busy (ignored or corrupted),
which manifests as TX_DONE never firing on DIO1 because the SX1262
never actually completed the SetTx it received during BUSY=high.

Fix per lora-rs/lora-rs#260: Pull::Down → Pull::None on BUSY.
Matches the official lora-rs nRF52840 examples.

Applied to both Wio Tracker L1 (reported broken by @swaits today) and
RAK4631 (currently works for us, but was affected by the same class
of bug per the upstream issue — this makes it deterministically
correct rather than 'happens to work').

src/board/rak_wisblock_4631.rs

@@ -113,7 +113,11 @@ impl LoRaBoard for Board {
 
         let reset = Output::new(p.P1_06, Level::High, OutputDrive::Standard);
         let dio1 = Input::new(p.P1_15, Pull::Down);
-        let busy = Input::new(p.P1_14, Pull::Down);
+        // BUSY has an internal 20 kΩ pull-up on the SX1262 die (datasheet
+        // p. 53); an MCU-side Pull::Down fights it and leaves the line at
+        // an indeterminate voltage, making wait_on_busy unreliable. See
+        // lora-rs/lora-rs#260.
+        let busy = Input::new(p.P1_14, Pull::None);
 
         let iv = GenericSx126xInterfaceVariant::new(reset, dio1, busy, None, None)
             .expect("SX1262 interface init");

src/board/wio_tracker_l1.rs

@@ -96,7 +96,11 @@ impl LoRaBoard for Board {
 
         let reset = Output::new(p.P1_07, Level::High, OutputDrive::Standard);
         let dio1 = Input::new(p.P0_07, Pull::Down);
-        let busy = Input::new(p.P1_10, Pull::Down);
+        // BUSY has an internal 20 kΩ pull-up on the SX1262 die (datasheet
+        // p. 53); an MCU-side Pull::Down fights it and leaves the line at
+        // an indeterminate voltage, making wait_on_busy unreliable. See
+        // lora-rs/lora-rs#260.
+        let busy = Input::new(p.P1_10, Pull::None);
 
         // RF switch: RXEN on P1.08 (GPIO, toggled by lora_phy), TX via DIO2 (SX1262 internal).
         let rx_enable = Output::new(p.P1_08, Level::Low, OutputDrive::Standard);