fix(lint): resolve flake8 warnings and exclude .claude directory

Remove unused xy_prev variable in cpf.py, unused imports in
test_setpoint.py, and add .claude to flake8 exclude list.

Author: cuihantao

.flake8

@@ -1,3 +1,3 @@
 [flake8]
-exclude = .git,__pycache__,build,dist,demos,cases,cards,versioneer.py,andes/_version.py,docs/source/conf.py,docs/source/_build,benchmarks,andes/pycode,scripts,.history,scratch
+exclude = .git,.claude,__pycache__,build,dist,demos,cases,cards,versioneer.py,andes/_version.py,docs/source/conf.py,docs/source/_build,benchmarks,andes/pycode,scripts,.history,scratch
 max-line-length=115

andes/routines/cpf.py

@@ -585,7 +585,6 @@ def _continuation(self):
         z = self._compute_tangent(lam, z)
 
         # previous converged point (for secant orientation)
-        xy_prev = None
         lam_prev = None
 
         for k in range(self.config.max_steps):
@@ -662,7 +661,6 @@ def _continuation(self):
             fail_count = 0
 
             # save previous point for secant
-            xy_prev = xy.copy()
             lam_prev = lam
 
             xy = np.concatenate([dae.x[:n].copy(), dae.y[:m].copy()])

tests/integration/test_setpoint.py

@@ -5,11 +5,8 @@
 - GroupBase.set_setpoint() / get_setpoint()
 """
 
-import logging
 import unittest
 
-import numpy as np
-
 import andes
 from andes.utils.paths import get_case