Avoid per-result byte array allocation in EvaluateFilter

[Copilot]

EvaluateFilter was calling attributeJson.ToArray() on every filtered VSIM result before passing to JsonDocument.Parse, allocating a new byte[] per result on the hot path.

Change

Replace the allocating parse with a zero-copy parse using Utf8JsonReader + JsonDocument.ParseValue:

// Before
using var jsonDoc = JsonDocument.Parse(attributeJson.ToArray());

// After
var reader = new Utf8JsonReader(attributeJson);
using var jsonDoc = JsonDocument.ParseValue(ref reader);

Utf8JsonReader accepts ReadOnlySpan<byte> directly, so ParseValue parses in-place without materializing an intermediate array, eliminating the per-result GC allocation on the VSIM post-filter path.

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