Workaround for Tapioca DSL with RuntimeGeneric

Since this `self.entity` needs RuntimeGeneric and it's evaluated by
`tapioca dsl` this is triggering an incompatible error with how
RuntimeGeneric works.

This PR addresses it by early returning in this method when Tapioca is
evaluating.

Not very elegant but it makes the trick

lib/public/repositories/base.rb

@@ -23,6 +23,8 @@ module Base
 
       sig { returns(T.untyped) }
       def self.entity
+        return nil if defined?(Tapioca)
+
         T.unsafe(const_get(:Entity)).inner_type[:fixed]
       end