Reads a header's values with key case-insensitivity. Always returns an array: empty if the header
is absent or explicitly undefined, a single-element array for single-valued headers, and the
full list for multi-valued ones (e.g. Set-Cookie). Numeric values (as node:http's
OutgoingHttpHeader permits for e.g. content-length) are stringified.
Reads a header's values with key case-insensitivity. Always returns an array: empty if the header is absent or explicitly
undefined, a single-element array for single-valued headers, and the full list for multi-valued ones (e.g.Set-Cookie). Numeric values (asnode:http'sOutgoingHttpHeaderpermits for e.g.content-length) are stringified.