Fix for overwriting LD_PRELOAD if it contains libscalene.so and other values

[elesiuta]

It looks like in some cases setup_preload gets called more than once, so it was adding libscalene.so to LD_PRELOAD the first time then later replacing LD_PRELOAD with just libscalene.so, this fixes that case.

[Copilot]

Pull Request Overview

This PR ensures that if setup_preload is called multiple times, existing LD_PRELOAD entries aren’t overwritten when they already include libscalene.so.

• Adds an elif branch to preserve the full LD_PRELOAD when it already contains libscalene.so
• Retains existing behavior of prepending libscalene.so only when it’s absent

Comments suppressed due to low confidence (1)

scalene/scalene_preload.py:74

• Add unit tests for the branch where LD_PRELOAD already includes libscalene.so to verify that existing values are preserved and not accidentally overwritten.

elif "LD_PRELOAD" in os.environ and new_ld_preload in os.environ["LD_PRELOAD"]: