scc_info: introduce scc_and_mark_filter

* spot/twaalgos/sccinfo.hh, spot/twaalgos/sccinfo.cc: Here.
* spot/twaalgos/genem.cc: Use it.
* python/spot/impl.i, python/spot/__init__.py: Add bindings.
* tests/python/genem.py: Test it.
* NEWS: Mention it.

python/spot/__init__.py

@@ -1244,3 +1244,12 @@ class twa_word:
         """
         from IPython.display import SVG
         return SVG(self.as_svg())
+
+
+# Make scc_and_mark filter usable as context manager
+@_extend(scc_and_mark_filter)
+class scc_and_mark_filter:
+    def __enter__(self):
+        return self
+    def __exit__(self, exc_type, exc_value, traceback):
+        self.restore_acceptance()

python/spot/impl.i

@@ -832,7 +832,6 @@ def state_is_accepting(self, src) -> "bool":
   std::string __str__() { return spot::str_psl(*self); }
 }
 
-
 %runtime %{
 #include <memory>