chore: refactor h || s || e logic to just s || e

[erhant]

Given a result & task-id tuple $(y, t)$ with node key-pair $(k_\text{priv}, k_\text{pub})$ and task key-pair $(d_\text{priv}, d_\text{pub})$ it suffices to simply do:

$$ \begin{align*} s \gets &\text{Sign}(k_\text{priv}, t || y) \\ e \gets &\text{Encrypt}(d_\text{pub}, y) \end{align*} $$

The admin node will verify as follows:

$$ \begin{align*} y \gets &\text{Decrypt}(d_\text{priv}, e) \\ &\text{Verify}(k_\text{pub}, s, t || y) \end{align*} $$