Generate a typed error hierarchy from the ErrorCode enum

[lineoffligbot]

Today every failure raises HTTP::StatusError from http.rb's :raise_error
feature. The parsed body is reachable via e.response.parse, but it is untyped,
undocumented, and the same class covers all 50 documented failure modes.

Amazon Ads publishes a closed enum, components/schemas/ErrorCode, with 50
values and a description for each:

ACTION_NOT_SUPPORTED, ACTIVE_RESOURCE_LIMIT_EXCEEDED, ARCHIVED_PARENT_CANNOT_CREATE,
ARCHIVED_RESOURCE_CANNOT_EDIT, BAD_REQUEST, CONFLICT, CONTENT_TOO_LARGE,
DUPLICATE_FIELD_VALUE_FOUND, FIELD_VALUE_IS_INVALID, FORBIDDEN, INTERNAL_ERROR,
NOT_FOUND, PAYMENT_ISSUE, PRODUCT_INELIGIBLE, RESOURCE_ID_NOT_FOUND,
TOO_MANY_REQUESTS, UNSUPPORTED_MARKETPLACE, ...

Because the enum is closed we can generate the classes at build time rather
than defining them at runtime:

module AmazonAds
  class Error < StandardError
    attr_reader :response
    def status = response&.status&.code
    def deconstruct_keys(keys) = { status:, code: }
  end

  module Errors
    # Archived resources cannot be edited.
    class ArchivedResourceCannotEdit < Error; end
    # There have been too many requests, please slow down your call rate.
    class TooManyRequests < Error; end
    # ...
  end
end

Generating beats runtime const_set here: the constants exist before the first
failure, they are greppable, they get RBS types, and each carries Amazon's own
description as a doc comment.

Implementation notes

• Envelope shapes differ across our specs. amazon_ads.json and
  marketing_stream.json use {code, message}; reporting.json uses
  {code, detail}. A builder needs to handle both.
• With retries: n, http.rb raises HTTP::OutOfRetriesError instead. That needs
  catching and rebuilding into the same hierarchy.
• Unknown or missing codes should fall back to the base Error rather than
  raising during error construction.

Prior art

Peddler does this dynamically (lib/peddler/error/builder.rb) because SP-API
error codes are open-ended strings. We have a fixed enum, so we get to do the
better version.