perf: Use LinkedHashSet instead of array backed collection in ObjectsStore

[wchill]

Fixes #97

ObjectsStore does not provide an API for random access, so there is no point in using a list or array because we get no benefit from constant-time random access, as long as we can guarantee ordering (which LinkedHashSet does). This speeds up add, remove, and contains operations from O(n) to O(1), which prevents the degenerate case mentioned in #97.

The underlying data structure is not exposed (because all accesses are proxied through ObjectsStore), so we don't need to worry about the extra functions that ObjectsList/ArrayCollection provides.

Speedup: approximately 4 minutes spent for decode/modify/encode/zipalign/sign total -> 26 seconds on a Ryzen AI 9 HX 370.