Handle warning with function passed as parameters instead of wrapping them in result

Before, warning was wrapped into the propageted result and mayde so warnings as the same type as errors and you add to be careful to maintain the error list while modifying the result.

Now, warnings as handled as "algebraic effect" by propagating an add_warning function in the pipeline that modifie a local list ref. Warnings are recovered after the processing using an get_warning to be treated.

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