optimize adptive avg pool

[jianyizh]

follows #1883, shape [4096,256,6,6] channel last with output shape [6,6] in torchbench alexnet can get ~4x improvement on bmg

[Copilot]

Pull Request Overview

This PR optimizes the adaptive average pool operation by introducing a vectorized implementation for channel-last memory format. The changes add vectorization support to improve memory access patterns and performance for 2D adaptive average pooling operations.

Key changes:

• Add vectorized kernel implementation for adaptive average pooling in channel-last format
• Replace the original channel-last kernel with the new optimized vectorized version
• Add necessary memory access utilities for vectorization support

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