Add decoder for Technoline Cost Control RC / Voltcraft Energy Count 3000 (ec3k) energy meter

[nospam2000]

I already implemented and slightly tested the decoding, you can find the merge request here: #3373

If anyone wants to test the current version or review the file src/devices/ec3k.c that would be highly welcome.
I can collect some testdata to test the decoding without the device.

Here the output from the command rtl_433 -f 868000k -s 1000k -d :00000002 -v -F json:rtl868.log -M time:iso:utc:usec -M protocol -M level -M stats -M bits:

{"time" : "2025-10-04T16:30:48.015280", "protocol" : 282, "model" : "Voltcraft Energy Count 3000", "id" : 48027, "power" : 51.100, "energy" : 758.149, "energy2" : 758.149, "mic" : "CRC", "time_total" : 64942080, "time_on" : 57786240, "power_max" : 186.500, "reset_counter" : 4, "flags" : 8, "mod" : "FSK", "freq1" : 868.183, "freq2" : 868.263, "rssi" : 1.264, "snr" : 25.068, "noise" : -25.068}
{"time" : "2025-10-04T16:30:50.887781", "protocol" : 282, "model" : "Voltcraft Energy Count 3000", "id" : 47858, "power" : 65.300, "energy" : 1022.611, "energy2" : 1022.611, "mic" : "CRC", "time_total" : 64942080, "time_on" : 64942080, "power_max" : 205.800, "reset_counter" : 4, "flags" : 8, "mod" : "FSK", "freq1" : 868.199, "freq2" : 868.279, "rssi" : 0.620, "snr" : 24.362, "noise" : -24.363}
{"time" : "2025-10-04T16:30:51.684070", "protocol" : 282, "model" : "Voltcraft Energy Count 3000", "id" : 10832, "power" : 0.400, "energy" : 975.181, "energy2" : 975.181, "mic" : "CRC", "time_total" : 64942080, "time_on" : 64942080, "power_max" : 427.900, "reset_counter" : 10, "flags" : 8, "mod" : "FSK", "freq1" : 868.190, "freq2" : 868.274, "rssi" : -2.578, "snr" : 21.115, "noise" : -23.693}
{"time" : "2025-10-04T16:30:53.065660", "protocol" : 282, "model" : "Voltcraft Energy Count 3000", "id" : 48027, "power" : 49.900, "energy" : 758.149, "energy2" : 758.149, "mic" : "CRC", "time_total" : 64942080, "time_on" : 57786245, "power_max" : 186.500, "reset_counter" : 4, "flags" : 8, "mod" : "FSK", "freq1" : 868.177, "freq2" : 868.266, "rssi" : 1.356, "snr" : 23.571, "noise" : -23.571}