edIsOnCurve function
Implementation
bool edIsOnCurve(EdPoint point) {
if (point.isInfinity) return true;
final x2 = (point.x * point.x) % ed25519P;
final y2 = (point.y * point.y) % ed25519P;
final left = (ed25519P - x2 + y2) % ed25519P;
final right = (BigInt.one + ed25519D * x2 % ed25519P * y2) % ed25519P;
return left == right;
}