[SIGMON-517] cache the result of the read_csv method to improve Validation notebook performance

Context

• While creating the validation notebook for the PIC2 and PNO analysis, I stumbled into crashes of the notebook kernel while calling the get_last_ref_start_end_time method

What was done

• cache the result of the read_csv method to avoid reading the csv file for every row of the validation notebook

QA

• template link to sonar issues:http://sonar/component_issues/index?id=_GROUP_%3A_ARTIFACT_#resolved%3Dfalse%7Cauthors%3D_PAIR1_%2C_PAIR2_
• code was unit tested, even though the real test was made by launching the validation notebook
• acceptance tests were written

Review objectives

• assessment of code quality