Move lru_cache definitions to __init__ (#21)

Using the lru_cache decorators on class methods, the ones that have a reference to `self`,
will also cache self. So we move it to the __init__ of the class

(DIS-2913)

dissect/regf/regf.py

@@ -60,6 +60,9 @@ def __init__(self, fh):
             log.debug(f"Hive {self.filename!r} is not undergoing any transactions.")
 
         self.hbin_offset = 4096
+
+        self.cell = lru_cache(4096)(self.cell)
+
         self._root = self.cell(self.header.root_key_offset)
 
     def root(self):
@@ -105,7 +108,6 @@ def parse_cell_data(self, data):
 
         raise NotImplementedError(repr(sig))
 
-    @lru_cache(4096)
     def cell(self, offset):
         return self.read_cell(offset)