⚡ optimize ConcurrentHashSet.IntersectWith to prevent ToHashSet allocations

[johnstrand]

⚡ What: Optimized ConcurrentHashSet<T>.IntersectWith to iterate other and collect matches into a sized set bounded by _dictionary.Count, short-circuiting when all elements are matched, avoiding unbounded ToHashSet() allocations when other is an IEnumerable<T>.
🎯 Why: Previously, if other was not an ICollection<T>, other.ToHashSet() was called, creating memory allocations proportional to the size of other.
📊 Measured Improvement: Eliminates allocations proportional to other.Count for non-ICollection<T> inputs down to at most _dictionary.Count matching elements, with fast short-circuiting when all local keys are found.

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PR created automatically by Jules for task 4274503267266574944 started by @johnstrand

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