feat: add ELECROW ThinkNode-M2 board support

ESP32-S3 + SX1262 + 1.3" SH1106 OLED + CP2102 UART bridge +
1000 mAh Li-Po. Pin map verified against Meshtastic's
variants/esp32s3/ELECROW-ThinkNode-M2. DIO3 TCXO at 3.3 V (vs 1.8 V
on Heltec), VEXT_ENABLE active HIGH (opposite polarity), dedicated
LORA_POWER_EN on GPIO48 sequenced before SPI init. Reuses the
existing async SH1106 driver at I2C address 0x3C.

Refactors hal::esp32s3::{init_spi,init_i2c} and board::esp32s3::init_radio
to accept generic GPIO bounds so ESP32-S3 boards with different pin
assignments can share the helpers. init_radio now takes a
TcxoCtrlVoltage parameter instead of hardcoding Ctrl1V8.

Incidental cleanups needed to make `just check-all` green:

- Replace the core::mem::forget(output) pattern with let _foo = ...;
  current esp-hal makes Output non-Drop, so forget is a no-op that
  trips clippy's forget_non_drop lint.

- Switch justfile xtensa builds from `cargo +nightly` with a RUSTC
  override to `cargo +esp` so the compiler and rust-src versions stay
  aligned. Public nightly's rust-src had drifted two months ahead of
  the esp fork and broke -Zbuild-std on core.

src/main.rs

@@ -44,7 +44,7 @@ cfg_if::cfg_if! {
     if #[cfg(any(feature = "rak_wisblock_4631", feature = "wio_tracker_l1", feature = "waveshare_rp2040_lora"))] {
         use defmt_rtt as _;
         use panic_probe as _;
-    } else if #[cfg(any(feature = "heltec_v3", feature = "heltec_v3_uart", feature = "heltec_v4"))] {
+    } else if #[cfg(any(feature = "heltec_v3", feature = "heltec_v3_uart", feature = "heltec_v4", feature = "elecrow_thinknode_m2"))] {
         use esp_backtrace as _;
         use esp_println as _;
     }
@@ -66,7 +66,7 @@ cfg_if::cfg_if! {
         async fn main(spawner: Spawner) {
             run(spawner).await;
         }
-    } else if #[cfg(any(feature = "heltec_v3", feature = "heltec_v3_uart", feature = "heltec_v4"))] {
+    } else if #[cfg(any(feature = "heltec_v3", feature = "heltec_v3_uart", feature = "heltec_v4", feature = "elecrow_thinknode_m2"))] {
         #[esp_rtos::main]
         async fn main(spawner: Spawner) {
             run(spawner).await;