fix: enable ESP-IDF HAL by default for LR2021 variant

Enables USE_ESPIDF_HAL in platformio.ini to ensure reliable SPI
communication on ESP32-C3 boards where SPIClass(0) may return zeros.

variants/nicerf_lr2021/platformio.ini

@@ -24,6 +24,8 @@ build_flags =
   -D RADIOLIB_EXCLUDE_SX126X=1
   ; LR2021 IRQ DIO pin (configurable — LR2021 supports any DIO pin for IRQ)
   -D LR2021_IRQ_DIO=9
+  ; Use ESP-IDF SPI HAL (Arduino SPIClass returns zeros on some ESP32-C3 boards)
+  -D USE_ESPIDF_HAL
 build_src_filter = ${esp32_base.build_src_filter}
   +<../variants/nicerf_lr2021>
   +<helpers/sensors>