Set Mnemonics for default operators to have deterministic tests

[pmprete]

The mnemonics being used are public so we can commit them, but they should never be used in production.

[Ignacio-87]

Is this change also related to an update in the key manager struct?
I’m asking because, as far as I understand, it should be built together with that change. Otherwise, some tests might not pass 🤔. But is passing...

[pmprete]

Is this change also related to an update in the key manager struct? I’m asking because, as far as I understand, it should be built together with that change. Otherwise, some tests might not pass 🤔. But is passing...
It's not an update as far as i know, key manager supports this https://github.com/FairgateLabs/rust-bitvmx-key-manager/blob/main/config/development.yaml#L3