Improve Line Class: Add Docstrings, Remove None Handling for path_arc, and Simplify Logic

[irvanalhaq9]

Overview: What does this pull request change?

1. In Line: Set default path_arc to 0, removed None Handling related to path_arc, and simplify _account_for_buff()
2. In Line: Add docstring

Motivation and Explanation

Explanation 1:

• Removed None Handling for path_arc: The need for handling None before was because it was set to be the default value of path_arc. By changing the default to float 0, handling None becomes unnecessary. This simplifies the logic and eliminates the check for None. Changing the type of path_arc to just float also aligns with the method signatures of set_points_by_ends() and _account_for_buff(), where the type hint for path_arc is float only.
• Removed Irrelevant TODO Comment: The TODO comment related to handling None for path_arc is removed, as it is no longer needed.
• Removed Redundant return statement.

Explanation 2:

• Added Docstrings: Docstrings have been added to improve code documentation and readability.
• Added Example Usage: Example usage has been added to the docstring.

Links to added or changed documentation pages

https://manimce--4223.org.readthedocs.build/en/4223/reference/manim.mobject.geometry.line.Line.html

Reviewer Checklist

• The PR title is descriptive enough for the changelog, and the PR is labeled correctly
• If applicable: newly added non-private functions and classes have a docstring including a short summary and a PARAMETERS section
• If applicable: newly added functions and classes are tested