add: animation curves support

[Gavin-Niederman]

A work-in-progress PR adding support for f-curves and a timeline NodeInput variant.

TODO:

• AnimationCurve (f-curves implementation based on Blender's system)
• Timeline NodeInput variant.

In the future, the timeline inputs can be hooked up to the timeline curve editor.

[gemini-code-assist]

Code Review

This pull request introduces an AnimationCurve implementation, featuring keyframe-based interpolation (Linear, Constant, and Bezier) and integration into the node graph system via new nodes and registry updates. Review feedback suggests refining the evaluation logic to clamp out-of-bounds values to the nearest keyframe for better consistency and optimizing keyframe insertion using binary search to improve performance and data validation.

[gemini-code-assist]

The evaluation logic for time values before the first keyframe returns 0.0, while evaluation after the last keyframe returns the last keyframe's value. For animation curves, it is more consistent to clamp to the first keyframe's value when evaluated before the start of the curve, ensuring that properties (like scale or opacity) don't unexpectedly jump to zero.

Suggested change

	if index == 0 {
	return 0.0;
	} else if index == self.keyframes.len() {
	// unwrap is safe because of the non-empty guard at the top
	return self.keyframes.last().unwrap().knot.y;
	}
	if index == 0 {
	return self.keyframes[0].knot.y;
	} else if index == self.keyframes.len() {
	// unwrap is safe because of the non-empty guard at the top
	return self.keyframes.last().unwrap().knot.y;
	}

[gemini-code-assist]

Sorting the entire keyframes vector after every push is inefficient (O(N log N)). Since the vector is already sorted, you can use binary_search_by to find the correct insertion point and use insert or replace the existing keyframe, which is O(N). Additionally, validating that knot.x is finite prevents issues with sorting and searching logic caused by NaN values.

Suggested change

	pub fn push_keyframe(&mut self, keyframe: Keyframe) {
	self.keyframes.push(keyframe);
	self.keyframes.sort_by(|lhs, rhs| lhs.knot.x.partial_cmp(&rhs.knot.x).unwrap_or(std::cmp::Ordering::Equal));
	}
	pub fn push_keyframe(&mut self, keyframe: Keyframe) {
	if !keyframe.knot.x.is_finite() {
	return;
	}
	let index = self.keyframes.binary_search_by(|kf| kf.knot.x.partial_cmp(&keyframe.knot.x).unwrap_or(std::cmp::Ordering::Equal));
	match index {
	Ok(idx) => self.keyframes[idx] = keyframe,
	Err(idx) => self.keyframes.insert(idx, keyframe),
	}
	}

[gemini-code-assist]

This test case should be updated to reflect the suggested clamping behavior for out-of-bounds evaluation (returning the first keyframe's value instead of 0.0).

Suggested change

	assert_eq!(single_kf.evaluate(0.0), 0.0);
	assert_eq!(single_kf.evaluate(0.0), 10.0);

[Keavon]

Note: I rebased your branch.