Use modern PHP standards

[runelaenen]

The current PHP SDK implementation lacks compatibility with modern PHP project standards, as it relies on outdated practices such as loose typing and the absence of namespaces. These limitations make it challenging to integrate the SDK effectively into new and modern PHP codebases that do follow the standards.

This Pull Request proposes a rewrite of the SDK to align it with modern PHP conventions and best practices.
Additionally, I propose expanding support to cover all available API endpoints in Gorse, as the current implementation only includes a limited subset. Before proceeding with this extended implementation, I would appreciate confirmation from the maintainer to ensure alignment with the project’s goals.

[runelaenen]

Before proceeding with this extended implementation, I would appreciate confirmation from the maintainer to ensure alignment with the project’s goals.

@zhenghaoz
I just want to make sure this is OK, as I see that there are 2 other PR's that have made some changes that are quite old and were never merged.

[zhenghaoz]

Thank you. I think other 2 pull requests are stale. New pull requests are welcomed.