Add 56 test cases covering:
- isTransientError: 13 cases for context errors, retryable MonitorErrors,
and standard error types (nil, Canceled, DeadlineExceeded, Timeout, etc.)
- shouldTryPortlessFallback: 14 cases for connection error patterns that
trigger port fallback (refused, reset, no such host, timeout variants)
- shouldAttemptFallback: 13 cases for timeout/deadline/canceled patterns
used in storage polling fallback
- classifyDLQReason: 8 cases for dead letter queue reason classification
(max_retry_attempts vs permanent_failure)
- Edge cases: 3 cases for overlapping error patterns and partial matches
First test file for these error classification utilities used in retry
and fallback decision logic.
