Add UnsupportedError for unsupported features and update raise_on_duplicate_keys! method

Author: ydah

lib/jwt/encoded_token.rb

@@ -62,7 +62,10 @@ def initialize(jwt)
     #
     # @return [self]
     # @raise [JWT::DuplicateKeyError] if duplicate keys are found during subsequent parsing.
+    # @raise [JWT::UnsupportedError] if the JSON gem version does not support duplicate key detection.
     def raise_on_duplicate_keys!
+      raise JWT::UnsupportedError, 'Duplicate key detection requires JSON gem >= 2.13.0' unless JSON.supports_duplicate_key_detection?
+
       @allow_duplicate_keys = false
       self
     end

lib/jwt/error.rb

@@ -55,4 +55,7 @@ class JWKError < DecodeError; end
   # The DuplicateKeyError class is raised when a JWT contains duplicate keys in the header or payload.
   # @see https://datatracker.ietf.org/doc/html/rfc7519#section-4 RFC 7519 Section 4
   class DuplicateKeyError < DecodeError; end
+
+  # The UnsupportedError class is raised when a feature is not supported by the current environment.
+  class UnsupportedError < StandardError; end
 end

lib/jwt/json.rb

@@ -21,8 +21,6 @@ def parse(data, allow_duplicate_keys: true)
         raise
       end
 
-      private
-
       def supports_duplicate_key_detection?
         return @supports_duplicate_key_detection if defined?(@supports_duplicate_key_detection)