Support linear paths for static line graphs

[harrisrobin]

StaticLineGraph currently always uses Bézier interpolation. Measured signals often need straight sample-to-sample segments so the curve does not imply unmeasured values.

Proposal: add an optional curve: "bezier" | "linear" prop, defaulting to bezier for compatibility.

[huytdps13400]

Implemented in #134. The PR adds curve="linear" for static graphs, keeps Bézier as the default, and includes path-generation/type regression tests plus an example update. Local tests, typecheck, package build, lint (0 errors), and Expo web export all pass.