Depthwise Conv2D2d optimization

[jagrit06]

Proposed changes

• Add new specialized kernel for small kernel (kernels size <= 7), small strides (strides <= 2) depthwise 2d convolutions
• Add related tests

Checklist

Put an x in the boxes that apply.

• I have read the CONTRIBUTING document
• I have run pre-commit run --all-files to format my code / installed pre-commit prior to committing changes
• I have added tests that prove my fix is effective or that my feature works
• I have updated the necessary documentation (if needed)

[jagrit06]

Here are some numbers from a M2 Ultra

Before:

 N,   H,   W,    C   kH,  kW,    O, strides, padding, groups,  dtype, time_pt, time_mx, diff%
 1, 512, 512,  128,   3,   3,  128,  (2, 2),  (1, 1),   128, float16,  0.6711,  1.2874, -47.87%
 1, 256, 256,  128,   7,   7,  128,  (1, 1),  (3, 3),   128, float16,  0.2140,  2.4399, -91.23%
ATTENTION ^^^^^^^
 1, 256, 256,  128,   3,   3,  128,  (1, 1),  (1, 1),   128, float16,  0.1640,  1.2861, -87.25%
ATTENTION ^^^^^^^
 1, 128, 128,  256,   7,   7,  256,  (1, 1),  (3, 3),   256, float16,  0.1242,  1.2306, -89.90%
ATTENTION ^^^^^^^
 1, 128, 128,  256,   3,   3,  256,  (1, 1),  (1, 1),   256, float16,  0.1044,  0.6541, -84.04%
ATTENTION ^^^^^^^

After:

 N,   H,   W,    C   kH,  kW,    O, strides, padding, groups,  dtype, time_pt, time_mx, diff%
 1, 512, 512,  128,   3,   3,  128,  (2, 2),  (1, 1),   128, float16,  0.6689,  0.1321, +406.28%
 1, 256, 256,  128,   7,   7,  128,  (1, 1),  (3, 3),   128, float16,  0.2141,  0.1829, +17.11%
 1, 256, 256,  128,   3,   3,  128,  (1, 1),  (1, 1),   128, float16,  0.1647,  0.1077, +52.85%
 1, 128, 128,  256,   7,   7,  256,  (1, 1),  (3, 3),   256, float16,  0.1244,  0.0987, +26.06%
 1, 128, 128,  256,   3,   3,  256,  (1, 1),  (1, 1),   256, float16,  0.1049,  0.0619, +69.41%

[awni]

This looks awesome!