perf: use vlb in FilterScopedAttributes and defer creation.

[TimothyMakkison]

Small improvement, saves around 2 MB in ScopedAttributeFilter.FilterScopedAttributes by deferring Dictionary creation and using ValueListBuilder

Before

After

[thomhurst]

Summary

Performance optimization that uses ValueListBuilder and defers Dictionary allocation in ScopedAttributeFilter, saving ~2 MB.

Critical Issues

None found ✅

The changes look good:

• Proper use of ValueListBuilder with stack allocation
• Dictionary deferred until scoped attributes are actually encountered
• Return type change from List to T[] is safe (internal API, all callers just enumerate)
• Dispose() correctly called on ValueListBuilder
• Aligns with Rule 4 (Performance First) - minimizes allocations in hot path

Suggestions

Minor: Stack allocation size
The initial stack buffer is [null,null,null,null] (4 elements). Consider using stackalloc T[8] instead for a more typical initial capacity that matches common scenarios, though 4 is fine if profiling shows it's sufficient.

Note: OrderBy allocation
One call site (EventReceiverOrchestrator.cs:244) uses .OrderBy() which allocates anyway. This isn't a blocker, but if optimizing that path later, consider sorting the array in-place or using ValueListBuilder's ability to insert in sorted order.

Verdict

✅ APPROVE - Solid performance improvement with no critical issues