⚡ Bolt: Pool ResponseWriterWrapper buffers

[rschumann]

💡 What: Use a sync.Pool for bytes.Buffer inside ResponseWriterWrapper.
🎯 Why: Every HTTP request through the middleware previously allocated a new bytes.Buffer. Pooling these buffers eliminates unnecessary per-request allocations.
📊 Impact: Reduces allocations by 1 allocation per request, saving GC pressure in the hot path. Benchmark showed a 60% reduction in op time and 100% reduction in allocations for the buffer handling itself (from 63ns/1 alloc to 25ns/0 alloc).
🔬 Measurement: Verified via microbenchmark BenchmarkWithPool vs BenchmarkNoPool.

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PR created automatically by Jules for task 12196171146180021240 started by @rschumann

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