Make NEVR and NEVRA classes hashable (#416)

Make NEVR and NEVRA classes hashable

It turns out __hash__() is not implicitly inherited.
Related to packit/packit-service#2497.

Reviewed-by: Laura Barcziová

Author: softwarefactory-project-zuul[bot]

specfile/utils.py

@@ -98,6 +98,9 @@ def __init__(
     def _key(self) -> tuple:
         return self.name, self.epoch, self.version, self.release
 
+    def __hash__(self) -> int:
+        return hash(self._key())
+
     def __lt__(self, other: object) -> bool:
         if type(other) is not self.__class__:
             return NotImplemented
@@ -172,6 +175,9 @@ def __init__(
     def _key(self) -> tuple:
         return self.name, self.epoch, self.version, self.release, self.arch
 
+    def __hash__(self) -> int:
+        return hash(self._key())
+
     def __lt__(self, other: object) -> bool:
         if type(other) is not self.__class__:
             return NotImplemented