Add pattern matching support to Net::HTTPExceptions

[baweaver]

This PR adds deconstruct_keys to the Net::HTTPExceptions module, enabling pattern matching on HTTP exception classes for cleaner error handling.

Usage

begin
  http.request(req)
rescue => e
  case e
  in HTTPRetriableError[response: res] if res.code == '503'
    retry_with_backoff
  in HTTPClientException[message: /not found/]
    handle_not_found
  in HTTPFatalError[response:]
    log_fatal_error(response)
  end
end

Implementation

• Added PATTERN_MATCHING_KEYS constant to HTTPExceptions module with keys: message, response
• Implemented deconstruct_keys following Ruby pattern matching best practices
• Applies to all exception classes: HTTPError, HTTPRetriableError, HTTPClientException, HTTPFatalError
• Tests wrapped in instance_eval with SyntaxError rescue for Ruby 2.6 compatibility