Raise minimum prism version and fix deprecations

Prism 0.28.0 introduced a few breaking changes. In order to keep our code
simple, we've raised the minimum dependency version for prism.

Gemfile.lock

@@ -3,7 +3,7 @@ PATH
   specs:
     spoom (1.3.2)
       erubi (>= 1.10.0)
-      prism (>= 0.19.0)
+      prism (>= 0.28.0)
       sorbet-static-and-runtime (>= 0.5.10187)
       thor (>= 0.19.2)
 

lib/spoom/deadcode/indexer.rb

@@ -151,10 +151,19 @@ def visit_constant_or_write_node(node)
         visit(node.value)
       end
 
+      sig { override.params(node: Prism::ConstantPathNode).void }
+      def visit_constant_path_node(node)
+        parent = node.parent
+
+        visit(parent) if parent
+        reference_constant(node.name.to_s, node)
+      end
+
       sig { override.params(node: Prism::ConstantPathWriteNode).void }
       def visit_constant_path_write_node(node)
-        parent = node.target.parent
-        name = node.target.child.slice
+        const_path_node = node.target
+        parent = const_path_node.parent
+        name = const_path_node.name.to_s
 
         if parent
           visit(parent)