Fix method redefinition and circular require issues

[kholdrex]

#999

This PR addresses two issues:

1. Method Redefinition: The user_parameter method was being defined multiple times in lib/clearance/configuration.rb. This has been fixed by changing attr_accessor to attr_writer, ensuring the method is defined only once.

2. Circular Require: Circular dependencies between lib/clearance.rb and lib/clearance/engine.rb have been resolved by rearranging the require statements to avoid circular loading.

[sej3506]

Thank you! Good catch with the user_parameter method(s)!