ESP32C6 Compatibility

[ndoo]

ESP32C6 requires NEED_LOOKAHEAD_ENUM but the existing ifdefs in SDI12.h skip it.

It seems like the ESP-IDF version ESP32C6 Arduino framework uses for my specific ESP32C6 board (Seeed XIAO ESP32C6) is above the version in SDI12.h resulting in NEED_LOOKAHEAD_ENUM not being set and compilation failing due to the enum being missing (similar to ESP8266/ESP32 build failures before adding support).

Is there a rationale for the existing ESP IDF version check? Is there a more portable/universal check?

My build environment in PlatformIO:

[env:xiao-esp32c6]
platform = https://github.com/mnowak32/platform-espressif32.git#boards/seeed_xiao_esp32c6
platform_packages = 
    framework-arduinoespressif32 @ https://github.com/espressif/arduino-esp32.git#3.0.2
    framework-arduinoespressif32-libs @ https://github.com/espressif/arduino-esp32/releases/download/3.0.2/esp32-arduino-libs-3.0.2.zip
framework = arduino
board = seeed_xiao_esp32c6