This allows the CREATE code to bork without the Serai router losing access to
the coins in question. It does incur overhead on the deployed contract, which
now no longer just has to query its balance but also has to call the
transferFrom, but its a safer pattern and not a UX detriment.
This also improves documentation.
CREATE was originally intended for gas savings. While one sketch did move to
CREATE2, the security concerns around address collisions (requiring all init
codes not be malleable to achieve security) continue to justify this.
To resolve the gas estimation concerns raised in the prior commit, the
createAddress function has been made constant-gas.
