Refactor due to the enshittification of guzzle

[mradcliffe]

Issue	Metadata
Type	task
Version	main

Problem/Motivation

Guzzle made the Client class (and most of its things) final, which means that a once useful way to extend a class is now useless for no reason. This could help remove the use of guzzle later on.

Proposed Resolution

• Adds a client property to XeroClient.
• Add public function XeroClientInterface::request(string $method, string|UriInterface $uri = '', array $options = []): ResponseInterface. This should create a Psr\Http\Message\RequestInterface instance probably from one of the from methods on Psr\Util or whatever.
  • Add a deprecated public function XeroClient::get(string|UriInterface $uri = '', array $options = []) because I mentioned get in the README. Maybe also a post and a put because those are used in Xero API.
• Add public static function XeroClientInterface::createWithConfig(array $config, array $options) that returns a XeroClient instance.
• Makes backwards-incompatible change to __construct method to only provide guzzle client.
• Updates to documentation

Additional Information

N/A

[mradcliffe]

Of course nothing works with Guzzle 7.