Assorted improvements for ethstore and ethkey (#6961)

* Testing many passwords for presale wallet.

* Add multiple threads.

* WiP: ethkey brain wallets recover.

* Refactor pre-sale-wallet cracking.

* Generate in multiple threads. Brain with prefix.

* Validate bain wallet phrase.

* Brain wallet recovery.

* Self-review fixes.

* Fix tests.

* More docs.

* Bump versions.

* Remove cmd_find from borked merge.

* Update wasm submodules.

* Use threadpool.