Avoid postinstall by using optionalDependencies for each platform

[sverrejoh]

Problem

The azureauth package downloads its binary via a postinstall script. This doesn't work with:

• pnpm 10+ - blocks lifecycle scripts by default for security
• yarn PnP - not recommended due to unplugging behavior
• --ignore-scripts - when lifecycle scripts are disabled for security
• Network issues - downloads outside the package fetch stage miss retry mechanisms, caching, and mirrors

Proposed Solution

Use npm's optionalDependencies with os and cpu fields - the same pattern used by esbuild, SWC, and sharp.

1. Create platform-specific packages (@azureauth/darwin-arm64, etc.)
2. List them as optionalDependencies in the main package
3. Package managers automatically install only the matching platform
4. Postinstall becomes a fallback for unsupported platforms

References

• esbuild implementation
• npm RFC: Platform-Specific Dependencies