fix: Evaluate retryCondition for transient network-level errors

[sunil-lakshman]

Summary
Fixes Delivery SDK retry behavior for transient network-level failures and wires up retryDelayOptions.customBackoff in the core retry handler.

Problem
In retryResponseErrorHandler, errors without an HTTP response (error.response is undefined) were rethrown immediately. That skipped retryCondition, so codes like ETIMEDOUT, ECONNRESET, and EPIPE were never retried even when customers configured a custom retryCondition in StackConfig.

retryDelayOptions.customBackoff was exposed on HttpClientParams but not used when computing retry delays.

Solution

1. Evaluate retryCondition first for no-response errors; retry when it returns true.
2. Preserve existing ECONNABORTED behavior: still returns the 408-style timeout error when retryCondition does not apply.
3. Add getRetryDelay() to honor customBackoff → retryDelay → 300ms default for:

Network-level retries via retryCondition

retryCondition-driven HTTP error retries

429/401 retries
(Rate-limit header delays via x-ratelimit-remaining / retry-after are unchanged.)

Impact

Improves reliability for long-lived connections behind proxies, load balancers, and CDNs, including intermittent timeouts reported on Azure, without requiring custom axios interceptors.

Version
1.4.0 — May 25, 2026

Test plan

Unit tests for ETIMEDOUT, ECONNRESET, EPIPE, ECONNABORTED + retryCondition

Unit tests for customBackoff delay

Existing rate-limit (x-ratelimit-remaining) and 429/401 retry tests pass

Publish @contentstack/core@1.4.0 and bump @contentstack/delivery-sdk dependency

[github-actions]

🔒 Security Scan Results

ℹ️ Note: Only vulnerabilities with available fixes (upgrades or patches) are counted toward thresholds.

Check Type	Count (with fixes)	Without fixes	Threshold	Result
🔴 Critical Severity	0	0	10	✅ Passed
🟠 High Severity	0	0	25	✅ Passed
🟡 Medium Severity	0	0	500	✅ Passed
🔵 Low Severity	0	0	1000	✅ Passed

⏱️ SLA Breach Summary

✅ No SLA breaches detected. All vulnerabilities are within acceptable time thresholds.

Severity	Breaches (with fixes)	Breaches (no fixes)	SLA Threshold (with/no fixes)	Status
🔴 Critical	0	0	15 / 30 days	✅ Passed
🟠 High	0	0	30 / 120 days	✅ Passed
🟡 Medium	0	0	90 / 365 days	✅ Passed
🔵 Low	0	0	180 / 365 days	✅ Passed

✅ BUILD PASSED - All security checks passed