refactor: use utility functions consistently across codebase

refactor: use utility functions consistently across codebase

Replace manual patterns with existing utility functions to improve DRY
compliance:

- Use isEmpty/isNotEmptyArray/isNotEmptyString instead of .length checks
- Use convertToInt/convertToFloat instead of Number.parseInt/Number
- Use roundTo instead of Math.round(x * N) / N
- Use ensureError in catch blocks for proper error type narrowing
- Add UNIT_DIVIDER_KILO, MILLISECONDS_PER_HOUR and
  DEFAULT_EXPONENTIAL_BACKOFF_JITTER_MS to Constants

Note: isEmpty/isNotEmptyString apply whitespace trimming, which
tightens validation for identifiers and configuration values.