Switch maybe_dense_stack calls from TensorDict to LazyStackedTensorDict

[c3-utsavdutta98]

Bug in _use_buffers = False, in the case of non-contiguous tensors. Updated all calls to TensorDict.maybe_dense_stack(...) to LazyStackedTensorDict.maybe_dense_stack(...)

Description

When using _use_buffers = False, the code invokes TensorDict.maybe_dense_stack instead of the LazyStackedTensorDict class, which is where the API is supported. This PR aims to fix this bug.

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You can use the syntax close #15213 if this solves the issue #15213

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[pytorch-bot]

🔗 Helpful Links

🧪 See artifacts and rendered test results at hud.pytorch.org/pr/pytorch/rl/2238

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[vmoens]

This is because you need tensordict nightly I believe, can you check if that fixes your bug?