Fix backup restore notification progress updates

[leodyversemilla07]

Fixes #3160

This updates backup restore progress notifications so the foreground worker notification is refreshed as restore progress advances. It also reuses the same restore progress notification payload for foreground and normal updates, and serializes restore progress and error mutations during concurrent restore work.

Tested:

• ./gradlew spotlessCheck testReleaseUnitTest verifySqlDelightMigration assembleRelease -Pinclude-telemetry -Penable-updater
• installed preview build on device
• verified restore notification text/progress updates during backup restore

Self-review:

• confirmed changes are limited to the backup restore notification flow
• confirmed the GitHub Actions-equivalent local build passes