Enable the `require-await` ESLint rule. Async functions without `await`
are just regular functions with extra overhead — marking them `async`
adds implicit Promise wrapping, can hide missing `return` statements,
and misleads readers into expecting asynchronous behavior where there is
none.
While fixing the violations, I removed unnecessary `async` keywords from
source files and from various test callbacks that never used `await`.
This PR improves `clientonly` start option with better code structure,
validation, and comprehensive test coverage.
### Changes
**Refactoring:**
- Improved parameter handling with explicit function parameter passing
instead of closure
- Added port validation (1-65535) with proper NaN handling
- Removed unnecessary IIFE wrapper (Node.js modules are already scoped)
- Extracted `getCommandLineParameter` as a reusable top-level function
- Enhanced error reporting with better error messages
- Added connection logging for debugging
**Testing:**
- Added comprehensive e2e tests for parameter validation
- Test coverage for missing/incomplete parameters
- Test coverage for local address rejection (localhost, 127.0.0.1, ::1,
::ffff:127.0.0.1)
- Test coverage for port validation (invalid ranges, non-numeric values)
- Test coverage for TLS flag parsing
- Integration test with running server
### Testing
All tests pass:
```bash
npm test -- tests/e2e/clientonly_spec.js
# ✓ 18 tests passed
