LoRa/STM32WL: adjust Rx window offset and duration

Those timings open Rx time windows covering 99.7% of the one expected
by the antenna while allowing 3ms for the Rx subsystem to start listening.

embassy-lora/src/stm32wl/mod.rs

@@ -260,10 +260,10 @@ impl From<embassy_stm32::spi::Error> for RadioError {
 
 impl<'d, RS> Timings for SubGhzRadio<'d, RS> {
     fn get_rx_window_offset_ms(&self) -> i32 {
-        -500
+        -3
     }
     fn get_rx_window_duration_ms(&self) -> u32 {
-        3000
+        1003
     }
 }