Fix SyntaxWarning in stabilizer_states.py docstring

\sqrt in a non-raw docstring is an invalid escape sequence in Python 3.12.
Escape to \sqrt — Sphinx renders it identically.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

Author: Stephanie Wehner

simulaqron/toolbox/stabilizer_states.py

@@ -36,10 +36,10 @@ def __init__(self, data=None, check_symplectic: bool = True):
 
         A qubit in the state :math:`|1>` can be created as ``StabilizerState([[0, 1, 1]])``.
 
-        The entangled state :math:`(|00> + |11>)/\sqrt(2)` can be created as
+        The entangled state :math:`(|00> + |11>)/\\sqrt(2)` can be created as
         ``StabilizerState([[1, 1, 0, 0], [0, 0, 1, 1]])``.
 
-        The entangled state :math:`(|01> + |10>)/\sqrt(2)` can be created as
+        The entangled state :math:`(|01> + |10>)/\\sqrt(2)` can be created as
         ``StabilizerState([[1, 1, 0, 0, 0], [0, 0, 1, 1, 1]])``.
 
         :param data: Can be one of the following: