Improve cncli-leaderlog.sh: strict mode, logging, VRF check, test mode

- Added `set -Eeuo pipefail` with ERR trap for safer execution under systemd
- Introduced structured logging with timestamps, log file, and lock file
- Added VRF signing key readability check
- Added `--test` mode with CSV override and optional forced email
- Made CSV writing atomic (write to tmp then move)
- Added timeout wrapper for long-running commands
- Added warnings if email is configured but mail binary is missing
- Preserved original user configuration variables for easy setup

Author: Brolloks