Implement 2048 tilt move

Problem: Implement a 2048 “tilt” (move) operation

You are given a 4×4 board for the game 2048. Each cell contains either 0 (empty) or a power of two (2, 4, 8, ...). When the player swipes in one of four directions (up, down, left, right), the board updates as follows:

1. Shift: All non-zero tiles move as far as possible in the swipe direction.
2. Merge: If two tiles with the same value collide during the move, they merge into one tile with value equal to the sum (i.e., doubled).
3. Single-merge rule: A tile can be merged at most once per move.
4. After merges, tiles continue shifting to fill gaps in the swipe direction.

Task

Implement a function that applies exactly one swipe (tilt) to the board.

Function signature (language-agnostic)

• Input:
• board: 4×4 integer matrix
• dir: one of {up, down, left, right}
• Output:
• The updated 4×4 board after the move

Examples

• Swipe left:
• [2, 0, 2, 4] → [4, 4, 0, 0]
• Swipe left (single-merge rule):
• [2, 2, 2, 0] → [4, 2, 0, 0] (not [8, 0, 0, 0])
• Swipe left:
• [4, 4, 4, 4] → [8, 8, 0, 0]

Constraints / Notes

• Board size is always 4×4.
• Only implement the tilt/move logic (no random tile spawning, no scoring required unless you choose to return it as an extra).
• Be careful with edge cases around multiple merges in a line and ensuring each tile merges at most once per move.