transformRecord({ a: 1, b: 2 }, v => v * 10) // → { a: 10, b: 20 }transformRecord maps values in a Record from one type to another while preserving all keys.
Challenge: Implement transformRecord<T extends Record<string, unknown>, U>(obj: T, fn: (key: keyof T, value: T[keyof T]) => U): Record<keyof T, U> transforming each value with access to both key and value.
transformRecord({ a: 1, b: 2 }, (k, v) => `${k}=${v}`)
// → { a: 'a=1', b: 'b=2' }