tests/eoc: use standard NPC in the EOC_run_eocs test

[andrei8l]

Summary

None

Purpose of change

The EOC_run_eocs test uses a dummy npc with no id that breaks assumptions in other parts of the code, as seen in this job run: that mission is assigned with no ID, but when this dummy NPC dies it fails the mission because its ID matches, then the (pointless) debug message shows up because we've already cleared missions on the avatar.

Describe the solution

Use a standard test NPC

Describe alternatives you've considered

Robustify test infra to ensure there's no stale state for any test unit?

Testing

../build_lto/cata_test --rng-seed 1731840727 "~[slow] ~[.],starting_items" doesn't trigger the error

Wait for LTO job to finish.

Additional context

Perfect example of why we need LTO and ASan jobs to run earlier. It would have taken me <5 minutes to track this down (instead of 2 hours) if CI had run the LTO job for #77359

[RenechCDDA]

Uh related, #72167

Since this has come up at least twice, maybe there are even better guard rails? I have no concrete suggestions though

[andrei8l]

Uh related, #72167

Same issue, yeah. But I had forgotten how to spawn test NPCs so I hacked it and it was bad.

Since this has come up at least twice, maybe there are even better guard rails? I have no concrete suggestions though

Nope, let's not hide blatant code errors with fallbacks.

[RenechCDDA]

I meant something like forcing the constructor call to always assign a relevant ID. i.e. it shouldn't be possible to get a NPC reference with an invalid ID without it already yelling.

I don't know if that's feasible though. Please ignore me if this sounds unreasonable.

I would also consider checking the NPC assignment ID when completing the mission, and specifically mentioning it in the debugmsg(to help with debugging). Though I can see that being undesirable.