Play a notification sound when the notification is cancelled

What's Changed

• Add CGO_ENABLED=0 build in CI by @thiagokokada in #11
• Minor improvements in flake.nix by @thiagokokada in #12
• Simplify nix files by @thiagokokada in #13
• Improve nix ci by @thiagokokada in #14
• Add bundle for macOS in nix builds by @thiagokokada in #15
• Implement notification sound for when the notification is cancelled by @thiagokokada in #16
• Reduce cpu usage by @thiagokokada in #17

Full Changelog: v0.5...v0.6