Add visitForGc to CompressionStream to fix zlib slow-path leak #6743

Performance Gate Passed

✅ 72 untouched benchmarks
⏩ 129 skipped benchmarks¹

_{Comparing gbedford/zlib-compression-stream-gc-tracing (1220935) with main (2ab8992)}

129 benchmarks were skipped, so the baseline results were used instead. If they were deleted from the codebase, click here and archive them to remove them from the performance reports. ↩