Fixes#18356
## Summary
Setting `LOG_LEVELS=debug,info,error,warn` crashes with `TypeError:
logLevels.map is not a function` because `CastToLogLevelArray` silently
returns `undefined` for invalid levels.
Now it throws a clear error message listing the invalid levels and valid
options:
```
Invalid log level(s): info. Valid levels are: log, error, warn, debug, verbose
```
## Changes
- Throw descriptive `Error` when invalid log levels are provided instead
of returning `undefined`
- Updated tests to verify the error message
## Test plan
- [x] All 8 existing tests passing
- [x] `"toto"` → throws `Invalid log level(s): toto. Valid levels are:
log, error, warn, debug, verbose`
- [x] `"verbose,error,toto"` → throws listing only `toto` as invalid
- [x] Valid levels (`log,error,warn,debug,verbose`) continue working as
before
