fix(evals): fix rails code to be able to handle overlapping rails ("irrelevant", "relevant"), switch to "NOT_PARSABLE" for unparable responses (#1373)

* Fixes bug in rails code, that doesn't remove characters, doesn't handle both rail values in rail

* fix tests for NOT_PARSABLE

* cleanup

* cleanup comments

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Co-authored-by: Mikyo King <mikyo@arize.com>