Add termination condition based on percentage of visited tiles for Car Racing

[VincenzoPalma]

Description

The environment will now end with terminated = True when the lap is completed after reaching the specified percentage of visited tiles.

Fixes #1269

Type of change

• Bug fix (non-breaking change which fixes an issue)
• This change requires a documentation update

Checklist:

• I have made corresponding changes to the documentation

[pseudo-rnd-thoughts]

@VincenzoPalma To clarify what was the previous behaviour when the agent had cross that the lap completion percentage and got to the end?

Could you train an agent using PPO from SB3 and share the training graphes of the old and new versions?

[VincenzoPalma]

@pseudo-rnd-thoughts The previous behavior in that scenario was that the environment would not terminate upon completing the lap but would instead continue until reaching the time limit, at which point it would end with truncated = True.

I will try and train an agent as you suggest as soon as i can.