Update godot-cpp to godot-4.2-stable

[dsnopek]

This PR originally updated to the latest in the 4.1 branch, but now that Godot 4.1 is no longer supported, this now updates godot-cpp to the godot-4.2-stable release.

One of the most important changes this includes is PR godotengine/godot-cpp#1313 which fixes #239, which is a crash that's caused when this GDExtension is used in a project with another GDExtension.

Marking as DRAFT for now, because this includes the changes from PR #272 so that CI will pass

Original description (before 2025-03-24):

This updates the godot-cpp used by this extension to the latest on godot-cpp's 4.1 branch.

This will mean that the extension will only be compatible with Godot 4.1.4 or later due to the updates to the extension_api.json. However, if it was important than it still worked with Godot 4.1.0 to 4.1.3, then it should be possible to compile with scons custom_api_file=path/to/extension_api.json where that JSON file is from Godot 4.1.0 - and we could even stash that extension_api.json in the repo? Anyway, just let me know if you'd like adjustments for that.

However, updating to the newest godot-cpp that will work with Godot 4.1 will include a whole bunch of bug fixes that have been cherry-picked since then.

For example, PR godotengine/godot-cpp#1313 which fixes #239

As well as other various memory leaks, crashes, build-system improvements, etc.

[dsnopek]

Hm, not sure why SCons is failing on the CI, it's working for me locally...

[dsnopek]

Per conversation on RocketChat, I've switched this to updating to godot-cpp's godot-4.2-stable tag (rather than the latest on the 4.1 branch)

Also, I've switched this to DRAFT because it includes the changes from PR #272 so that the CI will pass