⚡ Bolt: [performance improvement] Optimize collection processing in CacheoutViewModel

[acebytes]

• 💡 What: Replaced eager .filter operations with .lazy.filter before .reduce, and replaced .isEmpty checks on filtered arrays with .contains(where:).
• 🎯 Why: hasSelection and selectedSize are computed properties accessed frequently by the SwiftUI render loop. Prevents O(N) intermediate array allocations and turns an O(N) evaluation into an O(1) short-circuit evaluation.
• 📊 Impact: Eliminates redundant array allocations per render cycle and reduces evaluation time for hasSelection.
• 🔬 Measurement: Observe CPU profiles and memory allocations during UI state changes (checking/unchecking categories).

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PR created automatically by Jules for task 7229269388015716734 started by @acebytes

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