Remove memberAlternativesCache

[janedbal]

Project Info

Metric	Value
Result cache size	805 MB
Main process memory	4,283 MB
Total max memory (all)	27.05 GB
Total files	22,268

DeadCodeRule only measurements:

AMD Ryzen AI MAX+ 395

	Memory Usage	Time
With cache	766 MB	6.49s
No cache	582 MB	8.63s
Δ	−184 MB	+2.14s (33% slower)

Intel Core i7-1255U

	Memory Usage	Time
With cache	788 MB	10.70s
No cache	608 MB	14.83s
Δ	−180 MB	+4.13s (39% slower)

---

But the main takeaways is that it does not affect overall memory and not even max memory of the main process. The only case I found where it affects max memory of main process (but still far from overall memory) was in phpstan-src.