[Bugfix] Fix VecNorm eps usage

[lin-erica]

Description

In the documentation, eps in VecNorm is described to be the lower bound of std, but it is done before the sqrt() operation, meaning if eps = 0.0001 then the lower bound of std is 0.01. There is also an additional clamp in the return. I kept the clamp in the std so that it can be the same value when using to_observation_norm().

Motivation and Context

From reading the docstring, I set the eps based on my interpretation, but the actual value was different than I expected.

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[pytorch-bot]

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