⬆️ Update dependencies across project

Update dependencies across project to latest versions

This update brings several dependencies to their newer versions:

- git2: 0.19.0 → 0.20.0
- dirs: 5.0.1 → 6.0.0
- colored: 2.1.0 → 3.0.0
- rand: 0.8.5 → 0.9.0
- unicode-width: 0.1.13 → 0.2.0
- tiktoken-rs: 0.5.9 → 0.6.0
- strum & strum_macros: 0.26.* → 0.27.1
- ratatui: 0.28.0 → 0.29.0
- tui-textarea: 0.6.1 → 0.7.0

Also updates the random number generator implementation in messages.rs
to use rand::prelude::* and the new rand::rng() function.

Author: hyperb1iss