Simplify module_inject.transpose

[xbcReal]

Motivation

The transpose() helper in deepspeed/module_inject/utils.py (consolidated from duplicate definitions in #7934) currently performs a temp-buffer + copy_() rewrite of the input tensor's storage:

def transpose(data):
    with torch.no_grad():
        data = data.contiguous()
        data1 = data.transpose(-1, -2).reshape(-1)
        data.reshape(-1).copy_(data1)
        data1 = None
    return data.reshape(data.shape[-1], data.shape[-2])

This PR replaces the body with a one-liner:

def transpose(data):
    return data.transpose(-1, -2).contiguous()

Two reasons

1. Subtle memory waste on non-contiguous input.
When the input is non-contiguous, data = data.contiguous() silently allocates a new storage. The follow-up copy_() then writes into that fresh storage, not into the caller's original storage — so the "in-place" intent is already lost. Worse, the temporary data1 buffer pushes peak memory to 3N instead of the 2N that .contiguous() alone would incur.

load_checkpoint.py:132 is a concrete case: weight_partition can come from torch.split(tmp_data, dst_shape[dim1], dim=dim)[rank] and is non-contiguous when dim == 1.

2. The in-place rewrite is not relied on by any caller.
A full audit of every call site shows all callers use the return value and none depend on the side effect of mutating the input's storage:

#	Call site	Input source	Return used	Relies on side-effect
1	policy.py:154	tmp = sd[src_name]	yes	no
2	policy.py:157	tmp = sd[src_name]	yes	no
3	policy.py:159	result of _transpose(...).contiguous()	yes	no
4	policy.py:161	local tmp	yes	no
5	policy.py:181	torch.cat((q,k,v), dim=0)	yes	no
6	policy.py:184	same qkv_data	yes	no
7	policy.py:198	torch.cat((reg, gate), dim=0)	yes	no
8	load_checkpoint.py:83	sd[0][prefix+n].to(device)	yes	no
9	load_checkpoint.py:132	torch.split(...) / torch.cat(...)	yes	no

Behavior

Input	Old peak	New peak	Return semantics
Contiguous	2N	2N	unchanged for callers
Non-contiguous	3N	2N	unchanged for callers

Changes

• deepspeed/module_inject/utils.py: rewrite transpose() body; remove now-unused import torch.

No call site changes.

Tests

pre-commit run --files deepspeed/module_inject/utils.py passes locally (yapf, flake8, check-torchdist, license header, codespell).