gh-36899: some ruff fixes and error links in the graphs folder
    
this fixes some ruff warnings and add some ilnks for errors in the doc
in the graphs folder

### 📝 Checklist

- [x] The title is concise, informative, and self-explanatory.
- [x] The description explains in detail what this PR is about.
    
URL: #36899
Reported by: Frédéric Chapoton
Reviewer(s): David Coudert

Author: Release Manager

src/sage/graphs/base/c_graph.pyx

@@ -624,8 +624,8 @@ cdef class CGraph:
 
         OUTPUT:
 
-        - Raise a ``NotImplementedError``. This method is not implemented in
-          this base class. A child class should provide a suitable
+        - Raise a :class:`NotImplementedError`. This method is not implemented
+          in this base class. A child class should provide a suitable
           implementation.
 
         .. SEEALSO::
@@ -1267,7 +1267,7 @@ cdef class CGraph:
 
         OUTPUT:
 
-        - Raise ``NotImplementedError``. This method is not implemented at
+        - Raise :class:`NotImplementedError`. This method is not implemented at
           the :class:`CGraph` level. A child class should provide a suitable
           implementation.
 

src/sage/graphs/base/graph_backends.pyx

@@ -6,7 +6,7 @@ This module implements :class:`GenericGraphBackend` (the base class for
 backends).
 
 Any graph backend must redefine the following methods (for which
-:class:`GenericGraphBackend` raises a ``NotImplementedError``)
+:class:`GenericGraphBackend` raises a :class:`NotImplementedError`)
 
 .. csv-table::
     :class: contentstable

src/sage/graphs/bipartite_graph.py

@@ -1,5 +1,4 @@
 # autopep8: off
-# -*- coding: utf-8 -*-
 r"""
 Bipartite graphs
 

src/sage/graphs/bliss.pyx

@@ -396,9 +396,10 @@ cpdef canonical_form(G, partition=None, return_graph=False, use_edge_labels=True
       canonical graph of ``G`` or its set of edges
 
     - ``use_edge_labels`` -- boolean (default: ``True``); whether to consider
-      edge labels. The edge labels are assumed to be hashable and sortable. If
-      this is not the case (ie a ``TypeError`` is raised), the algorithm will
-      consider the string representations of the labels instead of the labels.
+      edge labels. The edge labels are assumed to be hashable and
+      sortable. If this is not the case (ie a :class:`TypeError` is
+      raised), the algorithm will consider the string representations
+      of the labels instead of the labels.
 
     - ``certificate`` -- boolean (default: ``False``); when set to ``True``,
       returns the labeling of G into a canonical graph

src/sage/graphs/digraph.py

@@ -1,4 +1,3 @@
-# -*- coding: utf-8 -*-
 r"""
 Directed graphs
 
@@ -3187,9 +3186,9 @@ def topological_sort(self, implementation="default"):
         """
         Return a topological sort of the digraph if it is acyclic.
 
-        If the digraph contains a directed cycle, a ``TypeError`` is raised. As
-        topological sorts are not necessarily unique, different implementations
-        may yield different results.
+        If the digraph contains a directed cycle, a :class:`TypeError`
+        is raised. As topological sorts are not necessarily unique,
+        different implementations may yield different results.
 
         A topological sort is an ordering of the vertices of the digraph such
         that each vertex comes before all of its successors. That is, if `u`
@@ -3269,7 +3268,8 @@ def topological_sort_generator(self):
         Return an iterator over all topological sorts of the digraph if
         it is acyclic.
 
-        If the digraph contains a directed cycle, a ``TypeError`` is raised.
+        If the digraph contains a directed cycle, a :class:`TypeError`
+        is raised.
 
         A topological sort is an ordering of the vertices of the digraph such
         that each vertex comes before all of its successors. That is, if u comes

src/sage/graphs/digraph_generators.py

@@ -74,7 +74,7 @@
 from sage.graphs.graph import Graph
 
 
-class DiGraphGenerators():
+class DiGraphGenerators:
     r"""
     A class consisting of constructors for several common digraphs,
     including orderly generation of isomorphism class representatives.

src/sage/graphs/domination.py

@@ -1,4 +1,3 @@
-# -*- coding: utf-8 -*-
 r"""
 Domination
 

src/sage/graphs/generators/basic.py

@@ -1,4 +1,3 @@
-# -*- coding: utf-8 -*-
 r"""
 Basic graphs
 
@@ -400,7 +399,7 @@ def CompleteGraph(n):
         G.set_pos({0: (0, 0)})
     else:
         G._circle_embedding(list(range(n)), angle=pi/2)
-    G.add_edges(((i, j) for i in range(n) for j in range(i + 1, n)))
+    G.add_edges((i, j) for i in range(n) for j in range(i + 1, n))
     return G
 
 def CorrelationGraph(seqs, alpha, include_anticorrelation):

src/sage/graphs/generators/chessboard.py

@@ -1,4 +1,3 @@
-# -*- coding: utf-8 -*-
 r"""
 Chessboard graphs
 

src/sage/graphs/generators/degree_sequence.py

@@ -1,4 +1,3 @@
-# -*- coding: utf-8 -*-
 r"""
 Graphs with a given degree sequence
 
@@ -98,8 +97,8 @@ def DegreeSequenceBipartite(s1, s2):
         True
 
     Some sequences being incompatible if, for example, their sums are different,
-    the functions raises a ``ValueError`` when no graph corresponding to the
-    degree sequences exists::
+    the functions raises a :class:`ValueError` when no graph corresponding
+    to the degree sequences exists::
 
         sage: g = graphs.DegreeSequenceBipartite([2,2,2,2,1],[5,5])                     # needs sage.combinat sage.modules
         Traceback (most recent call last):