[Feature] optimize PP overlap (#5735)

* update to fully overlap, still debugging

* improve interface

* fixed deadlock bug

* debug NaN loss

* (experimental) use one comm group for send_fw_recv_fw to fix NaN

* cleaned up interfaces; use one batch p2p for all

* clean up; removed the double p2p batch case

* p2p test passsed

* improve overlap: send fwd before backward

* [pre-commit.ci] auto fixes from pre-commit.com hooks

for more information, see https://pre-commit.ci

* tentatively use 2 p2p batches

* remove two p2p batches

* fix typos

* [pre-commit.ci] auto fixes from pre-commit.com hooks

for more information, see https://pre-commit.ci

* remove pp.sh

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Co-authored-by: Edenzzzz <wtan45@wisc.edu>
Co-authored-by: pre-commit-ci[bot] <66853113+pre-commit-ci[bot]@users.noreply.github.com>
Co-authored-by: root <root@notebook-c55824c0-7742-45e8-9591-c855bb77ad29-0.notebook-c55824c0-7742-45e8-9591-c855bb77ad29.colossal-ai.svc.cluster.local>