Add support for saving/loading statefiles

[noclone]

Describe your changes

• Add statefile support: save/restore the engine state as a JSON file

Issue ticket number and link if any

#1777

Checklist for finalizing the PR

• I have performed a self-review of my code
• I have added tests for new features and bugfixes
• I have added documentation for new features
• If it is a modifying the libf3d API, I have updated bindings
• If it is a modifying the .github/workflows/versions.json, I have updated docker_timestamp

AI Disclosure

• I did not use AI to generate any of the content of that pull request
• I used AI to generate code in that pull request, if yes please disclose which part of the code was generated and with which model.
• I used Opus 4.8 to generate the bindings. I reviewed each line and modified when necessary.

Continuous integration

Please write a comment to run CI, eg: \ci fast.
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[github-actions]

You are modifying libf3d public API! ⚠️Please update bindings accordingly⚠️!
You can find them in their respective directories: c, python, java, webassembly.

[noclone]

\ci fast

[mwestphal]

one design choice to discuss

[mwestphal]

questions and remarks

[mwestphal]

a question about the cli options behavior

[mwestphal]

One design question, then better for @Meakk to take a last design look before we get into deep review