gh-40915: some -> bool annotations for is_a* methods
    
mostly about "is_abelian", "is_absolute" and "is_affine"

### 📝 Checklist

- [x] The title is concise and informative.
- [x] The description explains in detail what this PR is about.
    
URL: #40915
Reported by: Frédéric Chapoton
Reviewer(s): Frédéric Chapoton, Vincent Macri

Author: Release Manager

src/sage/algebras/lie_algebras/abelian.py

@@ -98,7 +98,7 @@ def _construct_UEA(self):
         """
         return PolynomialRing(self.base_ring(), self.variable_names())
 
-    def is_abelian(self):
+    def is_abelian(self) -> bool:
         """
         Return ``True`` since ``self`` is an abelian Lie algebra.
 
@@ -159,7 +159,7 @@ def dimension(self):
         """
         return infinity
 
-    def is_abelian(self):
+    def is_abelian(self) -> bool:
         """
         Return ``True`` since ``self`` is an abelian Lie algebra.
 

src/sage/algebras/lie_algebras/free_lie_algebra.py

@@ -206,7 +206,7 @@ def _construct_UEA(self):
         """
         return FreeAlgebra(self.base_ring(), len(self._names), self._names)
 
-    def is_abelian(self):
+    def is_abelian(self) -> bool:
         """
         Return ``True`` if this is an abelian Lie algebra.
 

src/sage/algebras/lie_algebras/lie_algebra.py

@@ -1329,7 +1329,7 @@ def zero(self):
         """
         return self.element_class(self, self._assoc.zero())
 
-    def is_abelian(self):
+    def is_abelian(self) -> bool:
         """
         Return ``True`` if ``self`` is abelian.
 

src/sage/categories/affine_weyl_groups.py

@@ -136,7 +136,7 @@ def succ(pair):
                                                    post_process=select_length)
 
     class ElementMethods:
-        def is_affine_grassmannian(self):
+        def is_affine_grassmannian(self) -> bool:
             """
             Test whether ``self`` is affine Grassmannian.
 

src/sage/categories/category.py

@@ -745,7 +745,7 @@ def __classcontains__(cls, x):
             return False
         return any(isinstance(cat, cls) for cat in c)
 
-    def is_abelian(self):
+    def is_abelian(self) -> bool:
         """
         Return whether this category is abelian.
 

src/sage/categories/category_types.py

@@ -333,7 +333,7 @@ def _latex_(self):
 
 
 class AbelianCategory(Category):
-    def is_abelian(self):
+    def is_abelian(self) -> bool:
         """
         Return ``True`` as ``self`` is an abelian category.
 

src/sage/categories/finite_dimensional_lie_algebras_with_basis.py

@@ -1506,7 +1506,7 @@ def hypercenter(self):
             """
             return self.upper_central_series()[-1]
 
-        def is_abelian(self):
+        def is_abelian(self) -> bool:
             """
             Return if ``self`` is an abelian Lie algebra.
 

src/sage/categories/lie_algebras.py

@@ -555,7 +555,7 @@ def killing_form(self, x, y):
                 0
             """
 
-        def is_abelian(self):
+        def is_abelian(self) -> bool:
             r"""
             Return ``True`` if this Lie algebra is abelian.
 

src/sage/categories/modules_with_basis.py

@@ -178,7 +178,7 @@ def _call_(self, x):
             raise TypeError("%s\nunable to coerce x (=%s) into %s" % (msg, x, self))
         return M
 
-    def is_abelian(self):
+    def is_abelian(self) -> bool:
         """
         Return whether this category is abelian.
 

src/sage/categories/vector_spaces.py

@@ -184,7 +184,7 @@ class WithBasis(CategoryWithAxiom_over_base_ring):
 
         _call_ = ModulesWithBasis.__dict__["_call_"]
 
-        def is_abelian(self):
+        def is_abelian(self) -> bool:
             """
             Return whether this category is abelian.