Switch to libusb_package for backend initialization

[Josverl]

Replace the manual handling of libusb with the libusb_package, simplifying the backend initialization process on Windows and ensuring easier installation for users.

[codecov]

Codecov Report

❌ Patch coverage is 62.50000% with 3 lines in your changes missing coverage. Please review.
✅ Project coverage is 75.56%. Comparing base (98c1e0b) to head (a9a885f).

Files with missing lines	Patch %	Lines
mpflash/flash/stm32_dfu.py	62.50%	3 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #103      +/-   ##
==========================================
- Coverage   75.60%   75.56%   -0.05%     
==========================================
  Files          54       54              
  Lines        3033     3032       -1     
  Branches      489      488       -1     
==========================================
- Hits         2293     2291       -2     
- Misses        621      623       +2     
+ Partials      119      118       -1     

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