Improved "not implemented" errors

Improved "not implemented" error message following suggestion from aidge#111 (closed).

assigned to @olivierbichler

enabled an automatic merge when the pipeline for 0eedf7f6 succeeds

mentioned in issue aidge#111 (closed)

approved this merge request

mentioned in commit 757cab85

merged

added Enhancement label

changed milestone to %aidge - May 2024