feat(anvil/cast): mnemonic generation

[teddav]

Added some new options in Anvil and Cast to ease mnemonic generation.

Cast

Added a "new-mnemonic" (or nm) option to generate a new mnemonic and generate a requested number of accounts from the mnemonic.
Example: cast wallet nm --words 12 --accounts 6
Generates a 12 words mnemonic and displays the first 6 accounts derived from that mnemonic.

Anvil

Added 2 options:

• mnemonic-random to start Anvil with a randomly generated mnemonic
• mnemonic-seed to provide a seed that generates a mnemonic. Useful for testing so that the base accounts are always the same
  Examples:

anvil --mnemonic-seed 42
anvil --mnemonic-random

[teddav]

I'll update the doc once it's merged
https://book.getfoundry.sh/reference/cast/cast-wallet

[Evalir]

straightforward! some convo around output/commands:

[Evalir]

This is also gonna need a rebase—sorry, lots of moving parts right now!

[Evalir]

nice! pushed a smol commit to remove unwraps—thanks!