* Created some tests that fail due to #1476

* Fixes 1476 and other ways to create a log1mexp

* Reimplemented logmexpm1_to_log1mexp by tracking expm1 and then looking through the clients

* Absorbed the rewrite log1pexp_to_softplus into the new rewrite for log1mexp

* Fixed bug where I forgot to check whether result of is_neg was None or not before proceeding

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Co-authored-by: Luca Citi <lciti@ieee.org>