packages: Additional tests around shielded keys

[jurevans]

Someone on Discord has reported that when testing import of the same mnemonic in the extension, sometimes their Payment Address is different. I'm not sure how this could be possible, and we have existing tests that ensure that the keys must match for any given mnemonic.

So, I propose:

• Add additional tests to the @namada/crypto lib (Rust & Jest)
  • Imported mnemonic generates the same seed
  • Payment Address & Viewing Key match expected when deriving from seed
• Add additional tests to @heliax/namada-sdk package (we currently have one test mnemonic, will add more)
• Ensure these tests are being run in CI each time

Testing

• packages/crypto
  • yarn test-wasm:ci
  • yarn test
• packages/sdk
  • yarn test

[mateuszjasiuk]

LGTM!