support fp32 all_reduce and reduce_scatter

[sallyjunjun]

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Motivation

support fp32 all_reduce and reduce_scatter

Modification

add reduce_comm_dtype to decide whether use float32 or bfloat16 to compute tensor in all_reduce and reduce_scatter communication.

internlm using isp parallel with sp size 2, weight size 2. The loss is as follows:

Using bf16 reduce, compared with original code without this feature, the loss diversity is within 1e-2.
While using fp32 reduce, loss is different from bf16 reduce.

the tgs is as follows:

The following is 7B moe module, with pipeline parallel size 2.
loss:

tgs:

BC-breaking (Optional)

Does the modification introduce changes that break the backward compatibility of the downstream repositories?
If so, please describe how it breaks the compatibility and how the downstream projects should modify their code to keep compatibility with this PR.

Use cases (Optional)

If this PR introduces a new feature, it is better to list some use cases here and update the documentation.

Checklist

Before PR:

• Pre-commit or other linting tools are used to fix the potential lint issues.
• Bug fixes are fully covered by unit tests, the case that causes the bug should be added in the unit tests.
• The modification is covered by complete unit tests. If not, please add more unit test to ensure the correctness.
• The documentation has been modified accordingly, like docstring or example tutorials.

After PR:

• If the modification has potential influence on downstream or other related projects, this PR should be tested with those projects.
• CLA has been signed and all committers have signed the CLA in this PR.