Note: this is a temporary solution, should be replaced once reduce kernel
is natively supported on KL2

* refactor: simplify send, recv interfaces

* refactor: rm send_partial, recv_partial, all_gather_partial

* XPU support eager mode

* add unittest for XPU eager mode

* minor bugfix

* minor bugfix, test=kunlun

* correct copyright info

* 1. remove unsed vars/funcs
2. ProcessGroupBKCL inherit from ProcessGroupStream

* bugfix for fp16 in eager mode multi-card, test=kunlun

* rebase & fix a few issues

* use new processgroup interface, test=kunlun

* fix compile issue, test=kunlun