Feat: Add Simple Curve APY calculation

[murderteeth]

• Add and test a typescript implementation of y-exporter's Simple Curve APY calculation, found here
  https://github.com/yearn/yearn-exporter/blob/master/yearn/apy/curve/simple.py#L56

• Update getApyComputer to handle the type crv:
  https://github.com/yearn/dashboard_ui/blob/208a9fdf9bb3a48406dbec58646a8a7991069e10/src/apy/index.ts#L19