Fix #71: use wide events in queue and scheduler

[mishankov]

Closes #71

Summary

• refactor queue processor and worker lifecycle logging to build structured wide events with steps, counts, and shutdown metadata
• refactor scheduler runs to emit a per-run wide event with cron metadata and trace IDs
• add log.WriteEvent(...) as the package-level event emission path, with fallback to ordinary structured logs when a wide-event logger is not installed
• add focused event-shape tests for queue and scheduler internals
• replace remaining httptest.NewRequest(...) calls in touched baseline tests with httptest.NewRequestWithContext(...) so repo lint passes

Validation

• task check was run successfully before the final log.WriteEvent fallback adjustment
• no further automated tests were run after that last logging fix, per request; manual verification is expected

Code Review

• pre-PR review found one blocker: wide-event emission was a no-op under the default logger configuration
• fixed by making log.WriteEvent(...) fall back to standard structured logging when the default logger does not implement wide-event writing
• no remaining blocker findings after that fix

Notes

• default logging still works without requiring applications to install a dedicated wide-event logger
• wide-event output remains available when applications do install a compatible logger