Add simple methods to convert to and from bytes for ZZ and finite fields

src/sage/rings/finite_rings/element_base.pyx

@@ -143,7 +143,7 @@ cdef class FiniteRingElement(CommutativeRingElement):
             raise ValueError("unknown algorithm")
 
     def to_bytes(self, byteorder="big"):
-        """
+        r"""
         Return an array of bytes representing an integer.
 
         Internally relies on the python ``int.to_bytes()`` method.

src/sage/rings/finite_rings/finite_field_base.pyx

@@ -2118,7 +2118,7 @@ cdef class FiniteField(Field):
                 for col in B.columns()]
 
     def from_bytes(self, input_bytes, byteorder="big"):
-        """
+        r"""
         Return the integer represented by the given array of bytes.
 
         Internally relies on the python ``int.from_bytes()`` method.

src/sage/rings/integer_ring.pyx

@@ -1575,7 +1575,7 @@ cdef class IntegerRing_class(PrincipalIdealDomain):
         return pAdicValuation(self, p)
 
     def from_bytes(self, input_bytes, byteorder="big", is_signed=False):
-        """
+        r"""
         Return the integer represented by the given array of bytes.
 
         Internally relies on the python ``int.from_bytes()`` method.