Move lru_cache definitions to __init__ (#17)

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/squashfs/squashfs.py

@@ -46,6 +46,11 @@ def __init__(self, fh: BinaryIO):
         self.minor = self.sb.s_minor
         self.size = self.sb.bytes_used
 
+        self._read_block = lru_cache(1024)(self._read_block)
+        self._lookup_id = lru_cache(1024)(self._lookup_id)
+        self._lookup_inode = lru_cache(1024)(self._lookup_inode)
+        self._lookup_fragment = lru_cache(1024)(self._lookup_fragment)
+
         self._compression_options = None
         if (self.sb.flags >> c_squashfs.SQUASHFS_COMP_OPT) & 1:
             self._compression_options = self._read_block(len(self.sb))[1]
@@ -131,7 +136,6 @@ def _read_metadata(self, block: int, offset: int, length: int) -> tuple[int, int
 
         return block, offset, b"".join(result)
 
-    @lru_cache(1024)
     def _read_block(self, block: int, length: Optional[int] = None) -> tuple[int, bytes]:
         if length is not None:
             # Data block
@@ -162,21 +166,18 @@ def _read_fragment(self, fragment: int, offset: int, length: int) -> bytes:
         _, data = self._read_block(entry.start_block, entry.size)
         return data[offset : offset + length]
 
-    @lru_cache(1024)
     def _lookup_id(self, id: int) -> int:
         block, offset = divmod(id * 4, c_squashfs.SQUASHFS_METADATA_SIZE)
         _, _, data = self._read_metadata(self.id_table[block], offset, 4)
         return struct.unpack("<I", data)[0]
 
-    @lru_cache(1024)
     def _lookup_inode(self, inode_number: int) -> INode:
         if inode_number <= 0 or inode_number > self.sb.inodes:
             raise IndexError(f"inode number out of bounds (1, {self.sb.inodes}): {inode_number}")
         block, offset = divmod((inode_number - 1) * 8, c_squashfs.SQUASHFS_METADATA_SIZE)
         _, _, data = self._read_metadata(self.lookup_table[block], offset, 8)
         return self.get(struct.unpack("<Q", data)[0])
 
-    @lru_cache(1024)
     def _lookup_fragment(self, fragment: int) -> bytes:
         fragment_offset = fragment * len(c_squashfs.squashfs_fragment_entry)
         block, offset = divmod(fragment_offset, c_squashfs.SQUASHFS_METADATA_SIZE)