feat(releases): add GitHub release download utilities

Add generic GitHub release download utilities for cross-project use:

- downloadGitHubRelease(): Download releases from any GitHub repository
- downloadSocketBtmRelease(): Specialized wrapper for socket-btm releases

Features:
- Version caching with .version files to avoid redundant downloads
- Cross-platform binary downloads (darwin, linux, win32)
- Automatic platform/arch detection with musl support for Linux
- macOS quarantine attribute removal for downloaded binaries
- Generic asset downloads (WASM files, models, etc.)
- API inspired by industry tools (brew, cargo, gh) for intuitive usage

Package exports:
- @socketsecurity/lib/releases/github
- @socketsecurity/lib/releases/socket-btm

Note: Unit tests included but need mock refinement for HTTP requests

Author: jdalton