Feature/2.4.4 compatibility

[supercid]

Description

• Update PHP SDK
• Bump PHP min version to 7.4
• Suppress PHP 8.1 inheritance warning (since 7.4 does not have typehint return for mixed, which is needed)
• Little bit more strict types
• Better types in general

Related Issue

Not public

Motivation and Context

Magento 2.4.4 came with significant changes to how we handle the data schema, requiring removal of PHP based schema to XML.

How Has This Been Tested?

Tested locally with a brand new docker image for Magento 2.4.4 and PHP 8.1
You can test by using https://github.com/supercid/magento-docker-bin

• Clone the repo
• Run run_first_time.sh run_first_time.sh
• Feel free to test locally at https://magento2.dev.nos.to

Tested in plugintest at https://magento244.plugintest.nos.to/

Documentation:

No updates needed

Checklist:

• My code follows the code style of this project.
• I have updated the documentation accordingly.
• All new and existing tests passed.
• I have assigned the correct milestone or created one if non-existent.
• I have correctly labeled this pull request.
• I have linked the corresponding issue in this description.
• I have updated the corresponding Jira ticket.
• I have requested a review from at least 2 reviewers
• I have checked the base branch of this pull request
• I have checked my code for any possible security vulnerabilities