Initializes a new error with the given version conflicts. @param [{String => Resolution::Conflict}] conflicts see {conflicts} @param [SpecificationProvider] specification_provider see {specification_provider}

@return [String] An error message that includes requirement trees,

  which is much more detailed & customizable than the default message

@param [Hash] opts the options to create a message with. @option opts [String] :solver_name The user-facing name of the solver @option opts [String] :possibility_type The generic name of a possibility @option opts [Proc] :reduce_trees A proc that reduced the list of requirement trees @option opts [Proc] :printable_requirement A proc that pretty-prints requirements @option opts [Proc] :additional_message_for_conflict A proc that appends additional

  messages for each conflict

@option opts [Proc] :version_for_spec A proc that returns the version number for a

  possibility