cmd/clef: add importraw feature to clef

[holiman]

This adds importraw as a subcommand to clef.

Walking the happy-path:

[user@work clef]$ go run . --suppress-bootwarn importraw ./hexkey
INFO [10-28|14:03:08.718] Starting clef                            keystore=/home/user/.ethereum/keystore light-kdf=false
DEBUG[10-28|14:03:08.719] FS scan times                            list="61.22µs" set="72.06µs" diff="6.886µs"
## Password

Please enter a password for the imported account
> 
-----------------------
## Password

Please repeat the password you just entered
> 
-----------------------
DEBUG[10-28|14:03:15.040] FS scan times                            list="78.702µs" set="74.598µs" diff="6.765µs"
## Info 
Key imported:
  Address 0x9160DC9105f7De5dC5E7f3d97ef11DA47269BdA6
  Keystore file: /home/user/.ethereum/keystore/UTC--2022-10-28T12-03-13.976383602Z--9160dc9105f7de5dc5e7f3d97ef11da47269bda6

The key is now encrypted; losing the password will result in permanently losing 
access to the key and all associated funds!

Make sure to backup keystore and passwords in a safe location.

[holiman]

This PR now also adds clef CLI tests, covering the importraw, list-accounts and list-wallets commands. cc @jmcook1186