Fix classmethods in Python 3.13

Author: dstansby

numcodecs/zstd.pyx

@@ -28,8 +28,8 @@ cdef extern from "zstd.h":
 
     ZSTD_CCtx* ZSTD_createCCtx() nogil
     size_t ZSTD_freeCCtx(ZSTD_CCtx* cctx) nogil
-    size_t ZSTD_CCtx_setParameter(ZSTD_CCtx* cctx, 
-                                  ZSTD_cParameter param, 
+    size_t ZSTD_CCtx_setParameter(ZSTD_CCtx* cctx,
+                                  ZSTD_cParameter param,
                                   int value) nogil
 
     size_t ZSTD_compress2(ZSTD_CCtx* cctx,
@@ -235,7 +235,7 @@ class Zstd(Codec):
     """
 
     codec_id = 'zstd'
-    
+
     # Note: unlike the LZ4 and Blosc codecs, there does not appear to be a (currently)
     # practical limit on the size of buffers that Zstd can process and so we don't
     # enforce a max_buffer_size option here.
@@ -258,20 +258,17 @@ class Zstd(Codec):
              self.level)
         return r
 
-    @classmethod
     @property
-    def default_level(cls):
+    def default_level(self):
         """Returns the default compression level of the underlying zstd library."""
         return ZSTD_defaultCLevel()
 
-    @classmethod
     @property
-    def min_level(cls):
+    def min_level(self):
         """Returns the minimum compression level of the underlying zstd library."""
         return ZSTD_minCLevel()
 
-    @classmethod
     @property
-    def max_level(cls):
+    def max_level(self):
         """Returns the maximum compression level of the underlying zstd library."""
         return ZSTD_maxCLevel()