refactor: extract hal/ and driver/ modules

- Created hal/esp32s3.rs with MCU primitives (SPI, I2C, USB, UART, timer, MAC)
- Created hal/nrf52840.rs with shared nRF boilerplate (interrupts, bus wrapping, VBUS, MAC)
- Moved SH1106 OLED driver from display/ to driver/ (clear separation from app code)
- Board esp32s3.rs now delegates MCU init to hal, keeps only peripheral wiring (RadioParts)
- nRF board files use hal for shared StaticCell patterns, mac_address, interrupt bindings
- Board files still own pin assignments and peripheral construction

src/board/heltec_v3.rs

@@ -2,11 +2,12 @@ use esp_hal::gpio::{Level, Output, OutputConfig};
 
 use super::esp32s3;
 use super::traits::LoRaBoard;
+use crate::hal::esp32s3 as mcu;
 
 #[allow(unused_imports)] // Re-exported for other modules (display, radio, uart tasks)
 pub use super::esp32s3::{DisplayI2c, DisplayParts, RadioDriver, RadioParts, UartDriver, UartParts};
 
-// ── Board init ───────────────────────────────────────────────────────
+// ── Board init ──────────────────────────────────────────────────────
 
 pub struct Board {
     p: esp_hal::peripherals::Peripherals,
@@ -22,7 +23,7 @@ impl LoRaBoard for Board {
     }
 
     fn mac_address() -> [u8; 6] {
-        esp_hal::efuse::Efuse::mac_address()
+        mcu::mac_address()
     }
 }
 
@@ -30,16 +31,17 @@ impl Board {
     pub fn into_parts(self) -> (RadioParts, UartParts, Option<DisplayParts>) {
         let p = self.p;
 
-        esp32s3::start_timer(p.TIMG0);
+        mcu::start_timer(p.TIMG0);
 
         // Vext power: GPIO36, active LOW to enable peripherals
         let vext = Output::new(p.GPIO36, Level::Low, OutputConfig::default());
         core::mem::forget(vext); // hold pin low permanently; drop would reset it
 
-        let radio = esp32s3::init_radio(
-            p.SPI2, p.DMA_CH0, p.GPIO9, p.GPIO10, p.GPIO11, p.GPIO8, p.GPIO12, p.GPIO14, p.GPIO13,
-        );
-        let uart = esp32s3::init_uart(p.UART0, p.GPIO43, p.GPIO44);
+        let spi_bus = mcu::init_spi(p.SPI2, p.DMA_CH0, p.GPIO9, p.GPIO10, p.GPIO11);
+        let radio = esp32s3::init_radio(spi_bus, p.GPIO8, p.GPIO12, p.GPIO14, p.GPIO13);
+        let uart = UartParts {
+            driver: mcu::init_uart(p.UART0, p.GPIO43, p.GPIO44),
+        };
 
         // SSD1306 display reset: pulse GPIO21 low->high before I2C init
         let mut display_rst = Output::new(p.GPIO21, Level::Low, OutputConfig::default());
@@ -48,7 +50,7 @@ impl Board {
         esp_hal::delay::Delay::new().delay_millis(10);
         core::mem::forget(display_rst); // hold reset high permanently
 
-        let i2c = esp32s3::init_display_i2c(p.I2C0, p.GPIO17, p.GPIO18);
+        let i2c = mcu::init_i2c(p.I2C0, p.GPIO17, p.GPIO18);
         let mac = Self::mac_address();
         let display = Some(DisplayParts { i2c, mac });