[Fix] Overlapping duration validation

[ugurcanerdogan]

Description

This PR addresses a critical race condition issue where overlapping Listen() goroutines could be spawned if the configured WorkDuration exceeded the calculated cron interval.

Problem

Previously, if a user configured a WorkDuration that was longer than the interval between cron triggers (e.g., Cron: "Every 1 min", Duration: "2 mins"), the kafka-cronsumer would start a new listener goroutine while the previous one was still running. This led to:

• Race Conditions: Multiple consumers sharing the same resources.
• Message Duplication: Concurrent consumers processing the same messages.
• Potential Panics: Due to non-thread-safe operations in the underlying reader.

Solution

Instead of throwing a panic (which would be a hard breaking change) or allowing the unsafe behavior, we introduced a Smart Auto-Correction mechanism in the configuration validation phase:

1. Validation Logic: During startup, the Validate() method checks if Duration >= CronInterval.
2. Auto-Correction: If the duration exceeds the interval, it logs a WARNING and automatically sets the Duration to NonStopWork (0).
3. Safe Behavior: NonStopWork mode ensures that the consumer runs continuously in a single goroutine, which is the intended behavior when the duration is set to cover the entire interval (and more).

Changes

• Modified pkg/kafka/config.go: Added logic to parse the cron expression, calculate the interval, and apply the fix.
• Updated pkg/kafka/config_test.go: Added unit tests to verify that the auto-correction works as expected and invalid configurations are handled gracefully.

Example Scenario

Before:

Consumer: {
    Cron: "*/1 * * * *", // Every 1 minute
    Duration: 2 * time.Minute
}
// Result: Every minute a new goroutine starts. At T+1m, two goroutines run concurrently.

After (With this PR):

// Log: WARN: Consumer duration is greater than cron interval. It is set to NonStopWork (0) automatically.
Consumer: {
    Cron: "*/1 * * * *",
    Duration: 0 // (NonStopWork)
}
// Result: Single goroutine runs continuously without overlap.