Add OpenCL kernel for MultiBit wallets

[JosefZIla]

Hi, I've implemented GPU acceleration for MultiBit wallet password recovery using OpenCL. On my machine, it currently achieves a rate of approximately 4 million passwords per second:

(venv) [myd@neo btcrecover]$ python btcrecover.py --wallet wallet.key --tokenlist tokens.txt --enable-opencl --no-eta --dsw -d --opencl-workgroup-size 524288 --threads 8

Starting btcrecover 1.13.0-Cryptoguide on Python 3.13.3 64-bit, 21-bit unicodes, 64-bit ints
Notice: use --android-pin to recover the spending PIN of
    a Bitcoin Wallet for Android/BlackBerry backup (instead of the backup password)

OpenCL: Available Platforms
Platform 0 - Name NVIDIA CUDA, Vendor NVIDIA Corporation

OpenCL: Auto Selecting Best Platform
OpenCL: Using Platform: 0
OpenCL: Using Work Group Size:  524288

Wallet Type: btcrpass.WalletMultiBit
Wallet difficulty: 3 MD5 iterations
2025-07-27 14:27:10 : Using 8 worker threads
Duplicate Check Level: 1 , Add --no-dupchecks up to 4 times fully disable duplicate checking

\ 1943011328  elapsed: 0:07:54  rate:   4.09 MP/s

This is my first time working with OpenCL, so there may still be room for improvement and some rough edges. However, I've verified that the correct password is successfully identified.

[3rdIteration]

Great, thanks for the PR, I'll give it a test :)