`Eq` type class must take thunk-equality into account

[ivenmarquardt]

thunks are implemented as proxies in scriptum. The problem is that you cannot intercept ===/== with the proxy type, hence special care have to be taken to accept the following expression:

thunk(() => 2 * 3, "() => Number") === thunk(() => 2 * 3, "() => Number") === true