[numpy] Corrections de style et de terminologie

[Honaminto]

Summary

I went through numpy.md sentence by sentence, comparing it with the English version. In total I made 53 changes in the file, almost all style fixes to make the French read more naturally, plus one small bug fix.

What I changed

Most of my changes fix sentences that stuck too close to the English wording and sounded a bit forced in French. For example, I reworded phrases like "les tableaux disposent de méthodes utiles, toutes soigneusement optimisées" so it sounds more natural.

A few specific things:

• I made terminology more consistent in a few spots ("tableau plat" became "tableau unidimensionnel" in some sentences, to match the vocabulary already used elsewhere)
• I simplified a few clunky sentences in the exercises
• I reworded the intro note on broadcasting so it reads more smoothly
• I found and fixed a small bug: an {index} block was accidentally duplicated under Matrix Multiplication, so I removed the extra one

What I intentionally left alone

A few suggestions I didn't apply, because they either changed the technical meaning of the text or would have created inconsistency with terminology used elsewhere in the file. I also noticed a small mismatch between the text (which mentions tic/toc) and the code (which uses qe.Timer), but that comes from the English version, so I'll flag it as a separate issue instead of fixing it directly in the code.