perf: 1.21.9 roundabout collection

[Vonr]

No description provided.

[Noaaan]

What performance issue does this PR solve? Could you provide some description?
No need to do it twice for the 1.21 backport in #400

[Vonr]

sure, basically every time an ItemStack is copied, this gets called and there are multiple issues.

1. the stream usage is extremely inefficient when you can just grab the underlying keySet. 1.21.x does do it better with an ArrayList but even then it wasnt preallocating.
2. sometimes the collection isnt even necessary, but it happened anyways because the null check was located inside the receiving function.

overall this leads to some fairly ugly profiles