fix(traits): hand a trait its saved state back on load

[collindutter]

A save restored trait-rendered ui_options but left the live trait at its constructor defaults, so the editor could show max_val=50 while Slider still accepted 80. Stateful traits now expose plain save/load hooks, and the engine applies state to the instance built by node code so callbacks and other wiring remain intact:

class Threshold(Trait):
    def to_state(self) -> dict[str, int]:
        return {"level": self.level}

    def apply_state(self, state: dict[str, int]) -> None:
        if "level" in state:
            self.level = state["level"]

Closes #5440. Refs #5442.

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📚 Documentation preview 📚: https://griptape-nodes--5590.org.readthedocs.build/en/5590/

[codecov]

Codecov Report

❌ Patch coverage is 74.63977% with 88 lines in your changes missing coverage. Please review.

Files with missing lines	Patch %	Lines
...ptape_nodes/retained_mode/managers/node_manager.py	65.71%	12 Missing ⚠️
...pe_nodes/exe_types/param_types/parameter_button.py	18.18%	9 Missing ⚠️
...ape_nodes/exe_types/param_types/parameter_audio.py	0.00%	4 Missing ⚠️
...ape_nodes/exe_types/param_types/parameter_image.py	0.00%	4 Missing ⚠️
...tape_nodes/exe_types/param_types/parameter_json.py	0.00%	4 Missing ⚠️
...pe_nodes/exe_types/param_types/parameter_string.py	0.00%	4 Missing ⚠️
...ape_nodes/exe_types/param_types/parameter_video.py	0.00%	4 Missing ⚠️
...ptape_nodes/exe_types/param_types/parameter_xml.py	0.00%	4 Missing ⚠️
...tape_nodes/exe_types/param_types/parameter_yaml.py	0.00%	4 Missing ⚠️
src/griptape_nodes/traits/clamp.py	42.85%	4 Missing ⚠️
... and 16 more

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