fix: remove error when using Python >= 3.11 (#7)

Make Range immutable by adding __hash__ function. Needed to avoid errors using Python >= 3.11 triggered by the following change: https://docs.python.org/3.11/whatsnew/3.11.html#dataclasses

llvm_diagnostics/messages.py

@@ -33,6 +33,9 @@ def end(self):
         """Returns the last index of the Range"""
         return self.start + self.range
 
+    def __hash__(self):
+        return hash((self.start, self.range))
+
 
 @dataclass
 class __Message(Exception):  # pylint: disable=C0103