Added example to write a SDO

[ulikoehler]

Basic SDO write example using sdo_download. Complimentary to #56 and to the docs from #54 but neither are required to merge

Example:

$ cargo run --example write_sdo
[2025-11-02T13:23:02Z INFO  write_sdo] Opening EtherCAT master...
[2025-11-02T13:23:02Z DEBUG ethercat::master] Open EtherCAT Master /dev/EtherCAT0
[2025-11-02T13:23:02Z INFO  write_sdo] Writing SDO 0x6060:0 with value 0x06...
Wrote SDO 0x6060:0 = 0x06

Verified with AS715N servo drive. Reading back the value using #56 shows 0x06, previous: 0x01.

$ cargo run --example read_sdo
[2025-11-02T13:26:07Z INFO  read_sdo] Opening EtherCAT master...
[2025-11-02T13:26:07Z DEBUG ethercat::master] Open EtherCAT Master /dev/EtherCAT0
[2025-11-02T13:26:07Z INFO  read_sdo] Reading SDO 0x6061:0 [int8]...
SDO 0x6061/1 read int8 = 6