fix: bound on-failure restart attempts

[danielbaustin]

Fixes #318.

Summary

• count every unsuccessful on-failure exit toward a positive configured restart budget
• preserve attempts = 0 as the existing unbounded default
• stop resetting on-failure attempts during Started transitions while preserving reset behavior for other strategies
• transition to FinishedFailed after the configured retries are exhausted

With attempts = 3, Horust now performs the initial launch plus three retries, then exits with its documented failed-service status instead of continuing indefinitely.

Validation

• cargo fmt --all -- --check
• cargo test -p horust (all unit and integration sections passed; one existing ignored test)
• cargo test -p horust --test section_restart (5 passed)
• cargo clippy -p horust --lib --bins

The repository-wide all-target clippy command still reports pre-existing unused_io_amount findings in healthcheck test code and an existing dead-code warning in tests/utils; this patch does not touch those surfaces.