Add edge case tests for refactored make_line functions

[Copilot]

Adds comprehensive edge case tests for make_line_straight and make_line_angled functions introduced in the refactoring.

Test Coverage

make_line_straight (8 tests):

• Boundary slopes: horizontal (m=0), vertical (m=∞), diagonal (m=±1)
• Extreme slopes: steep (|m|>1), shallow (|m|<1)
• Grid boundaries and short 2-point lines

make_line_angled (11 tests):

• Cardinal angles: 0, π/2, -π/2, π
• All quadrants: π/4, 3π/4, -π/4, -3π/4
• Edge cases: zero length, boundary exceeding, angle wrapping (>2π)
• Grid size variations

All 19 tests validate current behavior including 1-indexed coordinates and grid boundary handling.

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