Auto merge of #29610 - mrobinson:notify, r=mukilan

Use notify-py to send notifications

- Use notify-py to send notifications, but use a custom notifier on
  Linux since transient (ie non-sticky) notifications are not supported.
- Add an icon to the notification.
- Don't send a notification after doing `./mach check` because that
  can trigger notifications when `rust-analyzer` is working.

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- [x] `./mach build -d` does not report any errors
- [x] `./mach test-tidy` does not report any errors
- [x] These changes do not require tests because they just change build notifications.

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