Lines with power operator `**` with simple operands are wrapped too early

[andersk]

Describe the bug

Black miscomputes the horizontal space required for lines containing the power operator ** with simple operands, and rewraps them much earlier than the expected 88-character line length. Perhaps that computation wasn’t adjusted for #538/#2726.

To Reproduce

Run Black with no arguments on this code (playground link):

x = 1**1**1**1**1**1**1**1**1**1**1**1**1**1**1**1**1
y = 1**1**1**1**1**1**1**1**1**1**1**1**1**1**1**1**1**1

Black leaves the first line unaffected, but unexpectedly wraps the second vertically, even though its horizontal layout is only 56 characters long.

x = 1**1**1**1**1**1**1**1**1**1**1**1**1**1**1**1**1
y = (
    1
    ** 1
    ** 1
    ** 1
    ** 1
    ** 1
    ** 1
    ** 1
    ** 1
    ** 1
    ** 1
    ** 1
    ** 1
    ** 1
    ** 1
    ** 1
    ** 1
    ** 1
)

Expected behavior

Both lines should be unchanged.

Environment

• Black's version: 23.9.1
• OS and Python version: Linux/Python 3.10.12