[REF] GENFI-To-BIDS : Separation of write_bids into 3 functions and tests added (#1538)

* separation of write_bids into 3 functions for genfi-to-bids + tests added

* modifs done after review

* corrections added after review

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Co-authored-by: ISMAILI Adam <[email protected]>
Co-authored-by: ISMAILI Adam <Adam ISMAILI>

Author: Adam-Ismaili-92