perf: optimize next 5 slowest nodes (Dilate3x3, Erode3x3, IntegralImage, ChannelCombine, CustomConvolution) #115

Job	Run time
build	1m 55s
Build rustVX (main)	1m 25s
Build Khronos OpenVX sample	48s
vision-arithmetic	23s
baseline	12s
vision-statistics	12s
graph	10s
vision-color	14s
vision-filters	1m 4s
vision-features	19s
vision-geometric	33s
vision-pyramid	13s
image-ops	10s
enhanced-vision (Phase 1 — Min/Max)	10s
KHR extension: user-data-object	13s
Perf gate (PR vs main)	2m 35s
data-objects	14s
Benchmark & compare (rustVX vs Khronos sample)	4m 47s
	15m 37s

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