Write sequentialPromises(items, asyncFn) function that executes an async function for each array element sequentially (one after another).

Requirements:

• Takes an array of items and an async function
• Calls asyncFn for each item in order
• Next call starts only after previous one completes
• Returns an array of all results in execution order
• If any call fails - stops and throws error
• Empty array returns []

Example:

const items = ['item1', 'item2', 'item3'];
const postData = async (item) => {
  await delay(100);
  return `posted: ${item}`;
};

const results = await sequentialPromises(items, postData);
// results = ['posted: item1', 'posted: item2', 'posted: item3']
// Total ~300ms (100ms * 3)