Description

Fix an issue where iterating over Cache.values threw a ConcurrentModificationError due to the underlying _mru list being updated.

Type of change

[x] Ran dart analyze or make analyze and fixed all issues
[x] Ran dart format --set-exit-if-changed -l 160 ./lib or make format and fixed all issues
[x] I have performed a self-review of my own code
[x] I have commented my code, particularly in hard-to-understand areas
[x] I have made corresponding changes to the documentation
[x] I have added tests that prove my fix is effective or that my feature works