[Enhancement] Generate vanity address or fingerprint on krux

[htprww]

This is an enhancement moved from the test release repro:
odudex/krux_binaries#3

This is more like a brainstorming idea about the possibility of krux.

We could allow the users to specify some prefix and/or postfix of the btc address or fingerprint they want.
Then krux will start from a random master key and try different keys until it finds a matched pattern of the address.

User could get a vanity address or fingerprint that is completely generated offline. So, the seed phrase should be safe to use.

Depending on the computing power of the krux devices, we could limit the length of the prefix and postfix.

I'm curious how long it usually takes to generate a new seed phrase and calculate the corresponding address and fingerprint.
If the whole process is fast enough on the krux device, we could make it run the process repeatedly until a vanity address/fingerprint is found.