text: Title: long string: black miscalculates line lengths (without string_processing)
  Body: **Describe the bug**
  
  In some cases the current black version (25.1.0) reformats a string that is too long. It seems to miscalculate the resulting line length.
  
  **To Reproduce**
  
  ```python
  class A:
      def foo(self):
          return (
              "This is a very loooooooooooooooooooooooooooooooooooooooooooooong string"
          )
  ```
  
  Note: The long line is exactly 86 chars wide. The bug does not occur when I add one character.
  
  ```sh
  $ black file.py
  ```
  
  reformats to:
  
  ```python
  class A:
      def foo(self):
          return "This is a very loooooooooooooooooooooooooooooooooooooooooooooong string"
  ```
  
  With the long line being 89 chars long.
  
  I would expect it to leave the code as is in this case.
  
  **Environment**
  
  - Black's version: 25.1.0
  - OS and Python version: Gentoo, Python 3.11.11
  
  **Additional context**
  
  The problem occurred first with in a project using `black -l100` producing a line of length 105.
  