Schniz/fnm: 🚀 Fast and simple Node.js version manager, built in Rust

fnm (Fast Node Manager) is a cross-platform Node.js version manager built in Rust, designed for speed and simplicity. It supports macOS, Windows, and Linux, works with existing `.node-version` and `.nvmrc` files, and can be installed via curl script, Homebrew, Winget, Scoop, Chocolatey, or Cargo. Shell integration is available for Bash, Zsh, Fish, PowerShell, and Windows Command Prompt, with automatic version switching via `--use-on-cd`. The README covers installation, shell setup, completions, configuration, and contributing instructions.