You are given an array of shopping order records. Each record looks like:

[
  { user: 8, total: 50, items: ['notebook'] },
  { user: 7, total: 150, items: ['pen'] },
  { user: 1, total: 10, items: ['eraser'] },
  { user: 7, total: 100, items: ['stapler', 'marker'] },
  { user: 7, total: 200, items: ['notebook'] },
  { user: 2, total: 200, items: ['pencil'] },
  { user: 2, total: 200, items: ['marker'] },
]

Each order has:

• user: User ID of the order
• total: Total cost of the order
• items: Array of purchased items (alphabetical order)

Your task: Implement mergeOrders(orders) to merge orders by user:

• Sum up totals for the same user.
• Combine item arrays (deduplicated + sorted alphabetically).
• Preserve order by keeping the first occurrence of each user.
• Do not mutate the original input.

Example

mergeOrders(orders);
// [
//   { user: 8, total: 50, items: ['notebook'] },
//   { user: 7, total: 450, items: ['marker', 'notebook', 'pen', 'stapler'] },
//   { user: 1, total: 10, items: ['eraser'] },
//   { user: 2, total: 400, items: ['marker', 'pencil'] },
// ]