update rust toolchain to 1.76

[LesnyRumcajs]

Summary of changes

Changes introduced in this pull request:

• updated Rust toolchain to 1.76.0
• removed const-random dependency; the macro started blowing up after the update, most likely to be resolved via Fix proc macro panicked with Invalid type in const_random! in Rust 1.77. tkaitchuck/constrandom#33. The resulting code ended up more straightforward anyway.

Reference issue to close (if applicable)

Closes

Other information and links

Change checklist

• I have performed a self-review of my own code,
• I have made corresponding changes to the documentation,
• I have added tests that prove my fix is effective or that my feature works (if possible),
• I have made sure the CHANGELOG is up-to-date. All user-facing changes should be reflected in this document.