Fix compatibility with Rails 8.0.0alpha

Decorating `class_attribute` has always been wonky.
I'm not 100% certain I'll go through with the Rails change,
but it's best if we don't rely on it.

We don't need to cache the file_path anyway.

CHANGELOG.md

@@ -1,5 +1,7 @@
 # Unreleased
 
+- Fix compatibility with Rails 8.0.0alpha: https://github.com/rails/rails/pull/52717
+
 # v0.27.2
 
 - Fix a Ruby warning that was emitted when `frozen_record` is loaded.

lib/frozen_record/base.rb

@@ -80,13 +80,6 @@ def primary_key=(primary_key)
         set_primary_key(-primary_key.to_s)
       end
 
-      alias_method :set_base_path, :base_path=
-      private :set_base_path
-      def base_path=(base_path)
-       @file_path = nil
-       set_base_path(base_path)
-      end
-
       attr_accessor :abstract_class
 
       def attributes
@@ -115,13 +108,11 @@ def current_scope=(scope)
 
       def file_path
         raise ArgumentError, "You must define `#{name}.base_path`" unless base_path
-        @file_path ||= begin
-          file_path = File.join(base_path, backend.filename(name))
-          if !File.exist?(file_path) && File.exist?("#{file_path}.erb")
-            "#{file_path}.erb"
-          else
-            file_path
-          end
+        file_path = File.join(base_path, backend.filename(name))
+        if !File.exist?(file_path) && File.exist?("#{file_path}.erb")
+          "#{file_path}.erb"
+        else
+          file_path
         end
       end