updateHeaders static method
Merges headers into the default headers sent on every request.
Use this when you need to update arbitrary headers (e.g. X-Tenant-Id,
Accept-Language) at runtime without re-initialising the service.
Existing keys are overwritten; all other headers are preserved.
NetworkService.updateHeaders({'X-Tenant-Id': tenantId});
Implementation
static void updateHeaders(Map<String, dynamic> headers) {
_apiManager.updateHeaders(headers);
}