Update pointmaze

[rodrigodelazcano]

Description

This PR adds some fixes to the PointMaze environments:

• Fix the calculation for the x, y simulation coordinates of the center of the maze
• Now, if a maze_map description is passed such that there are no "g", "r", or "c" cells, the initial goal and reset cells will be chosen randomly from the empty cells represented with 0. Read documentation for more information about the map data structure representation https://robotics.farama.org/envs/maze/point_maze/#maze-variations
• Add success key to infos return dictionary
• Reduce target success threshold from 0.5 to 0.45

Fixes # (issue)

Type of change

Please delete options that are not relevant.

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)
• This change requires a documentation update

Screenshots

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Checklist:

• I have run the pre-commit checks with pre-commit run --all-files (see CONTRIBUTING.md instructions to set it up)
• I have commented my code, particularly in hard-to-understand areas
• I have made corresponding changes to the documentation
• My changes generate no new warnings
• I have added tests that prove my fix is effective or that my feature works
• New and existing unit tests pass locally with my changes