refactor: simplify exclusive timeZone/utcOffset runtime check

[Gdhanush-13]

Problem

The CronTime initialization after the exclusive parameter check (#704) had a redundant third else branch:

if (timeZone != null) {
    this.cronTime = new CronTime(cronTime, timeZone, null);
} else if (utcOffset != null) {
    this.cronTime = new CronTime(cronTime, null, utcOffset);
} else {
    // Both are null/undefined here - same as the else-if result
    this.cronTime = new CronTime(cronTime, timeZone, utcOffset);
}

After the ExclusiveParametersError throw, both timeZone and utcOffset are guaranteed to not be non-null simultaneously. The third else branch is therefore always equivalent to the else if branch (both pass null/undefined), making it redundant.

Solution

Simplify to a ternary - timeZone != null is the only branch needed; the fallthrough handles all other cases:

this.cronTime =
    timeZone != null
        ? new CronTime(cronTime, timeZone, null)
        : new CronTime(cronTime, null, utcOffset ?? null);

No behavior changes - existing tests pass unchanged.

Fixes #704