fix(llcc68): align airtime estimate with radio config

Calculate LoRa airtime from the exact LDRO value supplied to SetModulationParams instead of inferring it from symbol time.

Keep transmit_result airtime in microseconds for both LoRa and GFSK, using integer Hz math and 64-bit ceil division to avoid truncation errors.

Reapply modulation parameters during async TX flush so the estimator and the bytes sent to the radio stay in sync, and add a compile-time check for the intended SF7/BW125 implicit 6-byte airtime.

include/llcc68.hpp

@@ -41,12 +41,13 @@ constexpr auto DEFAULT_BUSY_TIMEOUT_MS = 100;
  * @param preamble_length Preamble length in symbols
  * @param header_type Header type (implicit or explicit).
  * @param crc_type CRC type (none or 16-bit)
+ * @param ldro_on Low data rate optimization setting sent to the radio
  */
 constexpr airtime_t calc_time_on_air(uint8_t len, uint8_t sf, LoRaBandwidth bw,
-									 LoRaCodingRate cr,
-									 uint16_t preamble_length,
-									 LoRaHeaderType header_type,
-									 LoRaCrcType crc_type);
+                                     LoRaCodingRate cr,
+                                     uint16_t preamble_length,
+                                     LoRaHeaderType header_type,
+                                     LoRaCrcType crc_type, bool ldro_on);
 
 struct LLCC68 {
 	/** trivial getter */