np.unique now supports `sorted` param in future. Be explicit about it.

Part of the algorithm relies on `np.unique` returning sorted values. With the [new version](https://numpy.org/doc/stable/release/2.3.0-notes.html#performance-improvements-to-np-unique), we should be explicit(when possible)

https://github.com/cytomining/copairs/blob/0837962a2e743ebae0aa458a85777c6da7f1b76d/src/copairs/map/average_precision.py#L79

Read src/copairs/map/average_precision.py around line 79 and compare the current np.unique behavior with the linked NumPy 2.3 notes. Make the sorted-value assumption explicit where applicable, then run the relevant existing checks to confirm retrieval metrics are unchanged.

Written by the indexing model from the issue text.