chore(aafigure) Fix `SyntaxWarning` via literal string (fixes #6)

[tony]

Fixes #6.

Problem

lib/python3.12/site-packages/aafigure/aafigure.py:795
  /lib/python3.12/site-packages/aafigure/aafigure.py:795: SyntaxWarning: invalid escape sequence '\-'
    """\

-- Docs: https://docs.pytest.org/en/stable/how-to/capture-warnings.html

Changes

chore(_follow_rounded_edge): Use string literal for docstring

via "String and Bytes literals" in Lexical Analysis:

Both string and bytes literals may optionally be prefixed with a letter 'r' or 'R';