Implement progressive difficulty scaling based on score/time

[swathiiie]

Currently, the game maintains a fixed difficulty throughout gameplay. This makes long sessions predictable and reduces replay value.

GOAL:
Implement a dynamic difficulty scaling system that gradually increases game difficulty as the player progresses.

Proposed Enhancements:
Increase Pipe Speed Over Time
Gradually increase pipe movement speed every X seconds or after every Y score.
Example: Increase speed every 5 points.
Reduce Pipe Gap Slightly
Decrease the vertical gap between pipes progressively.
Ensure reduction is subtle to maintain playability.