Duplicated groups for EP and DP_EP

In MockNcclGroup, this line: https://github.com/aliyun/SimAI/blob/cee5b9f1d3806322e4a9912beb4d7778a93f179c/astra-sim-alibabacloud/astra-sim/system/MockNcclGroup.cc#L109
just repeats the group creation EP times, but keeps creating the same groups (with same ranks), as the j index is not used.
In my understanding, only one iteration should be enough for creating all the needed groups (i.e., _EP_nums).

A similar problem affects the DP_EP groups creation: https://github.com/aliyun/SimAI/blob/cee5b9f1d3806322e4a9912beb4d7778a93f179c/astra-sim-alibabacloud/astra-sim/system/MockNcclGroup.cc#L137

At last, this does not create a problem in the simulation run because there are just redundant groups (and they just keep replacing themselves in the GroupIndex structure, as the key is the same, eventually leaving only the last one there), but it creates a lot of confusion to me.

Start in astra-sim-alibabacloud/astra-sim/system/MockNcclGroup.cc at the EP group creation near line 109 and the DP_EP creation near line 137. Check how the j index is used and confirm that identical groups are being created repeatedly. Done means redundant group creation is removed while the simulation still creates the required groups and runs as before.