Optimize monotone interpolator by precomputing segment constants

## Context

A performance optimization opportunity was identified in the `createMonotoneInterpolator` function added in PR #8860.

## Suggestion

Precompute per-segment data (dx, m0dx, m1dx) to reduce the number of array reads and multiplications during interpolation evaluation. This would cache segment-level constants once during setup rather than recomputing them on every evaluation call.

## References

- PR: #8860
- Original suggestion: https://github.com/Comfy-Org/ComfyUI_frontend/pull/8860#discussion_r2838858980
- Suggested by: @christian-byrne

## File

`src/components/curve/curveUtils.ts`

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