`PreLiquidationAddressLib` is only used in `test` and should be moved their

[QGarchery]

We expect it to be useful to integrators, similarly to the periphery libraries on Morpho that are not used in the source files. Here, this lib would be useful notably to avoid trying to redeploy the pre-liquidation contract and having the transaction revert

[MathisGD]

Let's add it in the readme, because 1) people will not understand and 2) people will not find it.

[peyha]

Done in #65