[Algorithm] IMPALA and VTrace module

[albertbou92]

Description

This PR adds a VTrace module to be able to run IMPALA (https://arxiv.org/abs/1802.01561)

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[vmoens]

LGTM, can you edit the unused args?

[vmoens]

I don't see them appearing after that, so I would suggest to do

    def forward(
        self,
        tensordict: TensorDictBase,
        *, ...

for this and for GAE.