ENH: Prefer using visit_Constant

Prefer using `visit_Constant` instead of `visit_Num` and `visit_Str`:
both were deprecated since Python 3.8.

Fixes:
```
tract_querier/tests/test_query_eval.py: 40 warnings
tract_querier/tests/test_query_files.py: 6527 warnings
  /opt/hostedtoolcache/Python/3.9.20/x64/lib/python3.9/ast.py:407:
 DeprecationWarning: visit_Num is deprecated; add visit_Constant
    return visitor(node)
```

and
```
tract_querier/tests/test_query_eval.py: 1 warning
tract_querier/tests/test_query_files.py: 24 warnings
  /opt/hostedtoolcache/Python/3.9.20/x64/lib/python3.9/ast.py:407:
 DeprecationWarning: visit_Str is deprecated; add visit_Constant
    return visitor(node)
```

raised for example in:
https://github.com/demianw/tract_querier/actions/runs/12187495803/job/33998410948?pr=61#step:6:75
and
https://github.com/demianw/tract_querier/actions/runs/12187495803/job/33998410948?pr=61#step:6:80

Documentation:
https://docs.python.org/3/library/ast.html#ast.NodeVisitor.visit_Constant

tract_querier/query_processor.py

@@ -240,12 +240,6 @@ def visit_UnaryOp(self, node):
             raise TractQuerierSyntaxError(
                 "Syntax error in query line %d" % node.lineno)
 
-    def visit_Str(self, node):
-        query_info = FiberQueryInfo()
-        for name in fnmatch.filter(self.evaluated_queries_info.keys(), node.s):
-            query_info.update(self.evaluated_queries_info[name])
-        return query_info
-
     def visit_Call(self, node):
         # Single string argument function
         if (
@@ -558,31 +552,40 @@ def visit_Attribute(self, node):
                 (node.lineno, query_name)
             )
 
-    def visit_Num(self, node):
-        if (
-            node.n in
-            self.tractography_spatial_indexing.crossing_labels_tracts
-        ):
-            tracts = (
-                self.tractography_spatial_indexing.
-                crossing_labels_tracts[node.n]
+    def visit_Constant(self, node):
+        if isinstance(node.value, (int, float, complex)):
+            if (
+                node.n in
+                self.tractography_spatial_indexing.crossing_labels_tracts
+            ):
+                tracts = (
+                    self.tractography_spatial_indexing.
+                    crossing_labels_tracts[node.n]
+                )
+            else:
+                tracts = set()
+
+            endpoints = (set(), set())
+            for i in (0, 1):
+                elt = self.tractography_spatial_indexing.ending_labels_tracts[i]
+                if node.n in elt:
+                    endpoints[i].update(elt[node.n])
+
+            labelset = set((node.n,))
+            query_info = FiberQueryInfo(
+                tracts, labelset,
+                endpoints
             )
-        else:
-            tracts = set()
 
-        endpoints = (set(), set())
-        for i in (0, 1):
-            elt = self.tractography_spatial_indexing.ending_labels_tracts[i]
-            if node.n in elt:
-                endpoints[i].update(elt[node.n])
-
-        labelset = set((node.n,))
-        tract_info = FiberQueryInfo(
-            tracts, labelset,
-            endpoints
-        )
+        elif isinstance(node.value, str):
+            query_info = FiberQueryInfo()
+            for name in fnmatch.filter(self.evaluated_queries_info.keys(),
+                                       node.s):
+                query_info.update(self.evaluated_queries_info[name])
+        else:
+            raise NotImplementedError(f"{node.value} not supported.")
 
-        return tract_info
+        return query_info
 
     def visit_Expr(self, node):
         if isinstance(node.value, ast.Name):
@@ -735,6 +738,13 @@ def visit_Name(self, node):
             node
         )
 
+    # def visit_Constant(self, node):
+    #     if isinstance(node.value, str):
+    #         return ast.copy_location(
+    #             ast.Str(s=node.s.lower()),
+    #             node
+    #         )
+#
     def visit_Str(self, node):
         return ast.copy_location(
             ast.Str(s=node.s.lower()),