verify to be path independent

[Lewiscowles1986]

I've been trying to work on this, and I have noticed a lot of the scripts assume pwd or cwd matches the code.

Changing the verify_correctness.py to this, uses a little pathlib trick to get absolute paths to files on the system.

#!/usr/bin/env python3
"""
Verify correctness of the optimized Metal kernel
Compares against PyTorch reference implementation
"""

import sys
import numpy as np
from pathlib import Path

my_folder = Path(__file__).resolve().parent

# Initialize Metal with OPTIMIZED kernel
try:
    import _flash_attn_metal
    _flash_attn_metal.initialize()
    
    # Load common and OPTIMIZED kernel
    common_src = open(my_folder / 'kernels/common.metal').read()
    opt_src = open(my_folder / 'kernels/flash_attention_fwd_optimized.metal').read()

This means I can then run the verify_correctness.py outside of it's own folder, much like a regular package might run.

[Lewiscowles1986]

The same trick can work for test.py if you are interested in me submitting a PR, please let me know

[harvestingmoon]

Hi, yes feel free to submit a PR! i will take a look and verify it, if all is good will start merging it