itertools — Compose & Transform Iterators

Implement solve(lists, n) that:
1. Chains all sub-lists into a single sequence with itertools.chain.from_iterable.
2. Returns the first n elements that are even, as a list.

Use itertools.islice to avoid materializing the full sequence.

Examples

• solve([[1,2,3],[4,5,6],[7,8]], 3) → [2, 4, 6]
• solve([[1,3,5],[7,9]], 2) → [] *(no evens)*
• solve([[2,4,6,8]], 2) → [2, 4]

Constraints

• Do not use a plain for-loop to collect results — use itertools combinators.