Error Handling Enhancement

[skovtunenko]

Error Handling Enhancement
Current code doesn't expose error types. Add custom error types for better error handling:

// Create new file: errors.go
package graterm

type TerminationTimeoutError struct {
    Timeout time.Duration
}

func (e *TerminationTimeoutError) Error() string {
    return fmt.Sprintf("termination timed out after %v", e.Timeout)
}

// Update terminator.go Wait() method:
func (t *Terminator) Wait(appCtx context.Context, timeout time.Duration) error {
    // ... existing code ...
    case <-time.After(timeout):
        return &TerminationTimeoutError{Timeout: timeout}
    // ... rest of code ...
}

Or something like that