feat: add CurveInput wrapper class with interp method

[christian-byrne]

Summary

Demo PR targeting curve-node branch to show what the wrapper class + interpolation function should look like.

Changes

CurveInput class (comfy_api/latest/_input/basic_types.py):

• Wraps raw list[tuple[float, float]] control points
• interp(x): Monotone cubic Hermite interpolation matching the frontend createMonotoneInterpolator in curveUtils.ts
• to_lut(size): Generate a lookup table of evenly-spaced samples
• Pre-computes slopes on construction for efficient repeated evaluation

Type wiring:

• Curve.Type = CurveInput (under TYPE_CHECKING)
• Exported from comfy_api.input and comfy_api.latest._input

CurveEditor node:

• Now wraps raw widget points in CurveInput before outputting
• Handles both raw lists and already-wrapped CurveInput instances

Usage by downstream nodes

def execute(self, curve: io.Curve.Type):
    # Evaluate the curve at x=0.5
    y = curve.interp(0.5)
    # Generate a 256-entry LUT
    lut = curve.to_lut(256)
    # Access raw points
    points = curve.points

cc @jtydhr88 — this demonstrates the wrapper class and interp function we discussed. Feel free to merge into your branch or adapt as needed.

[jtydhr88]

I merged this and will add one more type of curve - linear, then make changes on FE