Fix Shift Amount in Proxy

[nlordell]

This PR fixes the shift amounts in the SafeProxy implementation. It also slightly optimizes how we do the masking by 2 instructions (removes the need to PUSH 0 and SHR).

I added some additional tests to make sure the masking works as expected and a comment explaining why we only mask for handling the masterCopy() call.

[nlordell]

@mmv08 - for some reason, the test is failing on zkSync. It looks like its related to some JS library issue, as there is a stack overflow happening (and looks to be caught in some infinite recursion).

I disabled the tests for now, but if you figure out what is going on feel free to enable them back in.

Figured it out, it looks like ContractFactory.deploy(...) doesn't resolve addresses in constructor args in the same way when zkSync is enabled :/