[ET-VK] Add alignment fields to PackedDimInfo for padded size calculation

[SS-JIA]

Stack from ghstack (oldest at bottom):

• [ET-VK][qconv] Add flexible layout impl for quantized pointwise conv #17221
• [ET-VK][testing] Create dedicated test binary for pointwise convolutions #17220
• [ET-VK][qconv] Add layout-agnostic general shader for quantized conv #17219
• [ET-VK][quantization] Add layout-flexible clone for int8x4 tensors #17171
• [ET-VK][qconv] Add layout-flexible impl of quantized depthwise conv2d #17108
• [ET-VK][ez] Implement helper functions to get fastest moving dim #17107
• [ET-VK][quantization] Implement layout-flexible quantize/dequantize operators #17106
• -> [ET-VK] Add alignment fields to PackedDimInfo for padded size calculation #17170
• [ET-VK][testing] Add per-shader timing breakdown to benchmark output #17105

This change introduces separate alignment fields to PackedDimInfo, decoupling
the alignment used for padding tensor dimensions from the block size used for
packing.

Previously, calculate_padded_sizes used packed_dim_block_size and
outer_packed_dim_block_size directly to determine how much to pad tensor
dimensions. This works but limits flexibility - there are scenarios where we
want to pad dimensions to a larger alignment than the block size for
performance reasons, such as ensuring loads are aligned to cache lines or
removing the need for bounds checking in shaders.

The new fields packed_dim_align and outer_packed_dim_align allow specifying
the alignment independently. For now, these are initialized to match the
corresponding block sizes, preserving existing behavior. Future changes can
set larger alignment values when beneficial for performance.

Authored with Claude.

Differential Revision: D92196649

[pytorch-bot]

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❌ 2 New Failures, 2 Pending

As of commit 121a290 with merge base 477867a ():

NEW FAILURES - The following jobs have failed:

• pull / test-vulkan-operators-linux / linux-job (gh)
  RuntimeError: Command docker exec -t e44815bca6eb252adcb42fc5f3507d86c2ad0e705372e5fa40976d1cfce47db8 /exec failed with exit code 134
• pull / unittest-editable / macos / macos-job (gh)
  backends/xnnpack/test/ops/test_conv2d.py::TestConv2d::test_fp16_conv2d

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