Add cargo-binstall support and adopt Rust target triple naming

[Muktarsadiq]

Summary

This PR adds support for cargo-binstall and transitions release assets to use Rust's standard target triple naming convention.

Changes

• Updated .github/workflows/cd.yml:

  • Added target triple mapping for release assets
  • Generates both new (Rust target triple) and legacy naming formats for backwards compatibility
  • Updated release notes to document the naming change

• Updated Cargo.toml:

  • Added package.metadata.binstall configuration pointing to the full variant

• Updated installation documentation:

  • Added cargo-binstall as the recommended installation method
  • Updated asset naming examples to use new format
  • Clarified architecture-specific download instructions

Migration Plan

• This release (0.4.2): Both naming formats available
• Next release: Remove legacy naming format

Testing

Users will be able to install spotifyd with:

cargo binstall spotifyd

Testing Note

Full end-to-end testing of cargo-binstall functionality requires a release with the new asset naming format. The workflow changes have been validated for syntax and logic, but actual installation testing will be possible after the first release with these changes.

I'm happy to help verify the installation works once a test release is created.

Closes #1200