Deep stringify the keys of the result params

[gsmendoza]

Fixes #110.

Summary

A error Braintree response would raise the following error:

Spree::LogEntry::DisallowedClass:
  Tried to dump unspecified class: Symbol

  You can specify custom classes to be loaded in config/initializers/spree.rb. E.g:

  Spree.config do |config|
    config.log_entry_permitted_classes = ['MyClass']
  end

Solidus Version:

3.4.0.dev

Cause

When SolidusBraintree::Response.build(result) accepts an error result, the result.params it passes to the new response has symbol keys. Here's a sample of the result.params:

    {:transaction=>
      {:amount=>"20.00",
       :order_id=>"R300000001",
       :channel=>"Solidus",
       :options=>{:store_in_vault_on_success=>"true"},
       :payment_method_token=>"0ev7m4dt",
       :customer_id=>"180763858",
       :type=>"sale"}}

Demonstration

See
https://github.com/solidusio/solidus_braintree/tree/gsmendoza/110-log-entry-disallowed-class-demo for a demonstration of the error and my attempts to fix it. Start from the "Try enabling venmo specs" commit.

Additional context

Related to #108.

There is also a PR in Solidus that will temporarily allow bad payloads to be saved in payment log entries. See
solidusio/solidus#4953

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