Update how nextLink value is retrieved

Currently the nextLink/after value is retrieved by removing the brackets and saving the contents. However, it is done by assuming that the brackets are in the first and last positions of the string. We need to update it to ensure that we do not delete any relevant information in case the brackets are not there.

Solutions:
1) Using `IndexOf` and `LastIndexOf` functions to check if the brackets exist and use their positions to delete them with regex (Similar to the way that it is done now)
2) Using only regex to only use the information found inside the brackets if they exist.

This task is made in reference to the following comment:
https://github.com/Azure/data-api-builder/pull/2893#discussion_r2413840792

Commencez par examiner la discussion de la pull request référencée et localiser le code qui récupère la valeur nextLink/after. Confirmez la gestion actuelle des crochets, puis vérifiez que les valeurs entre crochets sont extraites, tandis que les valeurs sans crochets conservent toutes les informations pertinentes.

Rédigé par le modèle d'indexation à partir du texte de l'issue.