minor cython code fixes

src/borg/compress.pyx

@@ -526,9 +526,10 @@ class Auto(CompressorBase):
             get_meta(cheap_meta, meta)
             return meta, cheap_compressed_data
 
-    def decompress(self, data):
+    def decompress(self, meta, data):
         raise NotImplementedError
 
+    @classmethod
     def detect(cls, data):
         raise NotImplementedError
 
@@ -562,7 +563,7 @@ class ObfuscateSize(CompressorBase):
     def _obfuscate(self, compr_size):
         # implementations need to return the size of obfuscation data,
         # that the caller shall add.
-        raise NotImplemented
+        raise NotImplementedError
 
     def _relative_random_reciprocal_obfuscate(self, compr_size):
         # effect for SPEC 1: