Bump version to 2.5.5

Preparing for release to PyPI.

Co-Authored-By: Claude Opus 4.5 <[email protected]>

Author: ChrisRackauckas

setup.py

@@ -5,7 +5,7 @@ def readme():
         return f.read()
 
 setup(name='diffeqpy',
-      version='2.5.4',
+      version='2.5.5',
       description='Solving Differential Equations in Python',
       long_description=readme(),
       long_description_content_type="text/markdown",