BIP-158: replace deprecated io/ioutil with os.ReadFile #1946

1. 
   strmfos commented at 11:12 am on August 28, 2025: contributor

   Update bip-0158/gentestvectors.go to use os.ReadFile instead of the deprecated io/ioutil package. The ioutil package has been deprecated since Go 1.16, with its functionality moved to the io and os packages.
2. BIP-158: replace deprecated io/ioutil with os.ReadFile 0712585a1c
3. 
   jonatack commented at 11:18 pm on September 2, 2025: member

   LGTM per sources like:

   • https://pkg.go.dev/io/ioutil?source=post_page-----bf3d03dfb454---------------------------------------#ReadFile
   • https://medium.com/@guptaunnati031/why-you-shouldnt-use-ioutil-package-in-golang-bf3d03dfb454
   • https://github.com/go-critic/go-critic/issues/1019
4. jonatack assigned Roasbeef on Sep 3, 2025

Contributors
strmfos jonatack