sagemathgh-36553: Add a hash function for the class TernaryQF.

PR from sagemath#16956 (rebased from https://github.com/sagemath/sagetrac-
mirror/commit/091cbbdf6eed2c8bccca407addd07ff08e429c17)

Author: Gustavo Rama

### 📝 Checklist

- [x] The title is concise, informative, and self-explanatory.
- [x] The description explains in detail what this PR is about.
- [x] I have linked a relevant issue or discussion.
- [x] I have created tests covering the changes.
- [x] I have updated the documentation accordingly.

URL: sagemath#36553
Reported by: Gonzalo Tornaría
Reviewer(s):

build/pkgs/configure/checksums.ini

@@ -1,4 +1,4 @@
 tarball=configure-VERSION.tar.gz
-sha1=aa7054a0e6a582d2db1475dc47f63a54e6ac569f
-md5=40eab024557ad51e08dfb08e2753a465
-cksum=802824779
+sha1=83682149aa0c33301f1742ef33fff6e95f7b099c
+md5=715e6e15ab579b997de55b6644af54f9
+cksum=363791132

build/pkgs/configure/package-version.txt

@@ -1 +1 @@
-c47788b02a42ef4907a0e61e702fbe9bbef27590
+4f15805fd81ea2a59964ce343faeaa353fd32c50

src/sage/quadratic_forms/ternary_qf.py

@@ -116,6 +116,19 @@ def coefficients(self):
         """
         return self._a, self._b, self._c, self._r, self._s, self._t
 
+    def __hash__(self):
+        """
+        Returns a hash for self.
+
+        EXAMPLES::
+
+            sage: Q = TernaryQF([1, 2, 3, 4, 5, 6])
+            sage: Q.__hash__()
+            5881802312257552497
+        """
+
+        return hash(self.coefficients())
+
     def coefficient(self, n):
         r"""
         Return the `n`-th coefficient of the ternary quadratic form.