Merges two Headers objects, respecting known single-value and multi-value headers.
If a single-value header appears in both, the value from the second Headers object will override the first.
Multi-value headers will combine values from both Headers objects, ensuring no duplicates.
Merges two Headers objects, respecting known single-value and multi-value headers. If a single-value header appears in both, the value from the second Headers object will override the first. Multi-value headers will combine values from both Headers objects, ensuring no duplicates.