Add compatability with php8.4

[craig-mcmahon]

This change prevents deprecations warnings such the following occurring when running on php 8.4

PHP Deprecated:  QuickBooksOnline\API\Core\OAuth\OAuth2\OAuth2LoginHelper::__construct(): Implicitly marking parameter $serviceContext as nullable is deprecated, the explicit nullable type must be used instead

This change requires php 7.1, but given that there is a requirement on guzzlehttp/guzzle version ^7.9 this implies a minimum version of php 7.2.5 which I have replicated in composer.json to make it clearer

[chas688]

ou guys should really merge this one in, as it fixes those issues with more current versions of PHP.

[kingIZZZY]

+1 Please merge this!

Otherwise getting these warnings in PHP 8.4:

DEPRECATED  QuickBooksOnline\API\Core\HttpClients\CurlHttpClient::__construct(): Implicitly marking parameter $curl as nullable is deprecated, the explicit nullable type must be used instead in vendor/quickbooks/v3-php-sdk/src/Core/HttpClients/CurlHttpClient.php on line 31.

DEPRECATED  QuickBooksOnline\API\Core\HttpClients\SyncRestHandler::__construct(): Implicitly marking parameter $client as nullable is deprecated, the explicit nullable type must be used instead in vendor/quickbooks/v3-php-sdk/src/Core/HttpClients/SyncRestHandler.php on line 53.

DEPRECATED  QuickBooksOnline\API\Core\OAuth\OAuth2\OAuth2LoginHelper::__construct(): Implicitly marking parameter $serviceContext as nullable is deprecated, the explicit nullable type must be used instead in vendor/quickbooks/v3-php-sdk/src/Core/OAuth/OAuth2/OAuth2LoginHelper.php on line 106.