Geometry improvements

[mathsvisualization]

Motivation

Currently, some methods were implemented only in Arrow even though they are
more general and applicable to all Line-based objects (including StrokeArrow).
This caused:

• Code duplication (same logic repeated in Arrow).
• Inconsistency (methods unavailable in StrokeArrow).
• Bugs (e.g., set_path_arc in Line did not behave correctly).

This PR moves/refactors these methods into the Line class so that they can be
reused consistently across all inheriting classes.

---

Proposed changes

• Moved reset_points_around_ends from Arrow → Line.
• Fixed and generalized set_path_arc in Line so that it works for both
  Arrow and StrokeArrow.
• Moved set_perpendicular_to_camera from Arrow → Line.
• Removed redundant implementations from Arrow.
• Added missing type hint import:

  from typing import Tuple

Code

from manimlib import *

class TestInsertLine(InteractiveScene):
    def construct(self):
        # Line with arc
        line = Line(LEFT, RIGHT, path_arc=PI, color=BLUE)
        line.always.set_perpendicular_to_camera(self.frame)
        self.add(line)
        line.set_path_arc(PI/2)

        # Arrow inherits Line functionality
        arrow = Arrow(LEFT, RIGHT, path_arc=-PI/4, color=RED)
        arrow.always.set_perpendicular_to_camera(self.frame)
        self.add(arrow)
        arrow.set_path_arc(-PI/2)

        # StrokeArrow also inherits Line functionality
        stroke_arrow = StrokeArrow(LEFT, RIGHT, path_arc=PI/3, color=GREEN)
        stroke_arrow.always.set_perpendicular_to_camera(self.frame)
        self.add(stroke_arrow)
        stroke_arrow.set_path_arc(PI/2)

Result:

• All three (Line, Arrow, and StrokeArrow) correctly reset around their ends.
• set_path_arc now applies consistently to both Arrow and StrokeArrow.
• set_perpendicular_to_camera works for all classes without duplication.